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Schwarzkopf BC Bonacure Smooth Perfect ShampooRs. 800250ml+Andis Slim Line BTF2 Cord & Cordless Rechargeable Trimmer for Men
Rs. 4,999Rs. 3,999
Rs. 5,798 Rs. 4,318.20 26% off Slashed discount Rs. 1000
Combo discount Rs.480
You Save: Rs. 1,480
1*Schwarzkopf BC Bonacure Smooth Perfect Shampoo + 1*Andis Slim Line BTF2 Cord & Cordless Rechargeable Trimmer for Men
Total Price: Rs. 5,79826% off
You Save: Rs. 1,480
Product Discount: Rs. 1,000
Combo Discount: Rs. 480
Final Price : Rs. 4,318.20
- Description
Quick Overview
Frizzy, flyaway and uncontrollable hair burning you out? Use Bonacure Smooth Control shampoo for smooth, manageable and lovely hair full of shine.By incorporating the new innovative IPS Complex and Amino Cell Rebuild technology hair is kept not only caressably soft with an illuminating shine but the inside of the hair is also repaired right down to the roots.
- Amino acid and natural oil are essential to smooth down and protect static and frizzy hair.
- Cleanses, nourishes and smoothes unmanageable hair and provides daily care while preventing frizz.
- So, say bye-bye to frizzy hair
How to use product
Apply shampoo and create lather by massaging the scalp gently. Rinse thoroughly.
Expiry Date : Click Here August 2019
All our products are far from expiry, and procured directly from the brand/authorized resellers of the brand.
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By Jagyoseni Mandal
This shampoo is very effective. Give this a shot.
Posted on 1/30/2017
By PRIYANKA
I really loved this shampoo. It leaves my hair smooth and soft after the wash. This shampoo is good for both thin hair and thick hair.
Posted on 1/28/2017
By Ekta Singh
I just simply love this shampoo...
Posted on 1/27/2017
By Meenakshi
Schwarzkopf BC Bonacure Smooth Perfect Shampoo
I have rebonded hair. So this shampoo works really well for me.. It makes my hair soft and non frizzy. the fragrance is mild.
Posted on 1/23/2017
By likitha
First time I order this shampoo..this was amazing..very smooth..I loved it..
Posted on 1/6/2017
By Shanjana Das
It has a very light fragrance. Good for dry damaged hair..
Posted on 1/3/2017
By sheetal
It made my hair smooth and shine ...
Posted on 12/6/2016
By Padma
I wud love to recommend this product to evry1 who are looking for a new shampoo which wud make their hair smooth n frizz free..i lv this shampoo,thnx to nykaa
Posted on 12/2/2016
By tanu
I am very impressed with this product. My basic problem is that I have oily scalp but my hair is dry. So I was confused what kind of shampoo is suitable for my hair. Thank god I got this bottle.! This shampoo is thick and creamy and it comes in a sleek white bottle with purple base with a flip cap.
Posted on 12/1/2016
By Smita Daftuar
Shampoo is good and effective for Hair. I am using it and will recommend for all. Fragrance is light.
Posted on 11/18/2016
Ask Nykaa (0)
Have a question on this product? Write a question and earn 100 reward points.Q.I have recently got Schwarzkopf smoothing done. Can I use this product?Question by: Aanchal on Jan 9, 2017 7:42:00 PMQ.I am a breast feeding mom and am looking for best anti hair fall shampoo and conditioner. Please help.Question by: Sweety on Aug 11, 2016 11:21:00 AMA.Thanks for writing to us.
For hairfall, you can try this product: http://www.nykaa.com/schwarzkopf-bc-bonacure-hair-activator-tonic.html?root=search&searchterm=Schwarzkopf&type=product&ptype=product
To know more about shampoos that reduce hairfall, see this link below: http://beautybook.nykaa.com/freedom-from-hair-fall-forever/
Hope that you find the solution to your advantage.
Thank you for shopping at Nykaa!
Team Nykaa
Answer by: Team Nykaa on Aug 12, 2016 2:41:44 PMQ.My hairs is curly and rough. After washing, it becomes fluffy and difficult to manage. Could you please suggest some products to make it smooth and shiny?Question by: Ms. Ashu Rani on Feb 18, 2016 11:04:00 AMA.Hi,
You need to use a good shampoo and conditioner meant for your hair type. Follow up with a serum and also deep condition your hair at least once a week. Our product recommendations are below:
We hope you've found a solution to your problem. Enjoy shopping at Nykaa.
Team Nykaa
Answer by: Team Nykaa on Feb 27, 2016 12:05:26 PMA.Thank you for the question.
Yes this shampoo is sulphate free. Infused with mild foaming system which is made using Coconut as base ingredient provides gentle cleansing. With Apricot kenel it smoothes hair surface and gives a shiny finish to hairs. Panthenol provides necessary moisture. Hope that you find the solution to your advantage.
Answer by: Team Nykaa on Sep 8, 2015 12:36:02 PM


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Flamefrost Legacy brings to your computer an epic RPG experience. Inspired by the d20 system and developed by an indie team Epic Dragon thanks to crowdfunding. In Flamefrost Legacy the player can choose between 3 races, the half-dragons Tul'Rhax, dwarfs and, of course, humans. Also there are 3 classes available, mage, warrior and rogue.
FlameFrost is a free to play isometric turn-based MMORPG that can be played directly in your browser, inspired by the table-top game "Dungeons & Dragons", as well as a number of old-school RPGs (such as "Icewind Dale" and "Baldur's Gate").
Explore the world map at your own pace, find new places, missions and enemies. Your character stats improve depending on what skills you are using, so for example you can improve your swordsmanship skill simply by using a sword during combat.
You can enjoy the DnD system of Flamefrost Legacy anywhere, as this game doesn't require any installation. So be prepared to throw fireballs on any device and wherever you are!

subset: commoncrawl


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VIDEO: Giannis Antetokounmpo with a fun dunk against Lithuania
Το κ?ρφωμα του Γι?ννη Αντετοκο?νμπο με τη... by 22ios
Milwaukee Bucks forward Giannis Antetokounmpo kind of gets treated like a puppy or a toddler. Since the internet loves his personality and his game so much, we tend to overhype what he does on a basketball court as "great" no matter how basic the play was. It's just weird seeing a 6'11" guy who is all limbs doing shooting guard type of plays, so perhaps it's the optical illusion he provides on the court adding to the entertainment of each play he completes.
While playing for Greece in the warm-ups to the FIBA World Cup in Spain at the end of this month, Antetokounmpo took the pass in the middle of the floor on a fast break, went up for the two-handed dunk, and swung around on the rim to ensure he'd land safely. Lithuanian forward Mindaugas Kuzminskas gave a soft attempt at trying to block the dunk, but never really got that into the picture.
I'm not sure this was a great dunk but it certainly was fun.
(H/T - BallinEurope.com)


text: Scion books Category page 11,088pages on this wiki Add New Page Edit Classic editor History Talk0 Scion: Hero Scion: Demigod Scion: God Liberty Road Scion: Ragnarök Scion Companion "April 18: Scion: Scion: Hero September 12: Scion: Scion: Demigod Scion books Seeds of Tomorrow Pages in category "Scion books" The following 8 pages are in this category, out of 8 total. L Liberty RoadS Scion books Scion Companion S cont. Scion: Demigod Scion: God Scion: Hero S cont. Scion: Ragnarök Seeds of Tomorrow Retrieved from "http://whitewolf.wikia.com/wiki/Category:Scion_books?oldid=42243" Ad blocker interference detected! Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers Wikia is not accessible if you've made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected. Categories: Game Books Scion Add category Cancel Save


text: To play golf well, as major Big Easy shareholder Ernie Els would tell you, you need more than a powerful, accurate drive (Els's "Big Easy"), you also need a combination of guile and inspiration to get from fairway to green and then, of course, forensic putting. In other words, you need the complete game. In restaurant terms the complete game... More


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Wright State University Libraries' Special Collections and Archives welcomes you to our blog. Join us as we share information, news, and special events; highlight our collections; and discuss archival issues. For more information:
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Category Archives: Local History
Archives Find: Civil War Bounty Request
By Andrew Clinard, archives student worker & Public History graduate student This document, issued through the Ohio Adjutant Generals Office in 1864, states that Sylvester Sroufe re-enlisted on January 1st, 1864, in Company D of the 12th Ohio Volunteer Infantry … Continue reading
Posted in Civil War, Collections, Local History, SC&A Tagged 12th Ohio Volunteer Infantry, 12th OVI, Andrew Clinard, Civil War, local history, manuscripts Leave a comment
It was on Jeopardy!
Last Tuesday I was watching "Jeopardy!" to cheer on Wright State senior Emily Bingham. Not only was I excited about Emily's impressive performance earning her a spot in tomorrow night's semi-finals, but I was also excited that one of the … Continue reading
Young Love in the Archives
Inspired by Valentine's Day, I want to share an item that I first saw in the archives years ago while researching an exhibit on children. When I opened a folder in the Schenck Family Papers (MS-284), I discovered a pink … Continue reading
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Welcome to the Arlington Country Day baseball team wall. The most current information will appear at the top of the wall dating back to prior seasons.
Utilize the left navigation tools to find past seasons, game schedules, rosters and more. Best of luck this spring!
Nominate a current Junior for the 2017 Semper Fidelis All-American Program, Presented by the Marines.
Florida has 12 players on the two rosters; Hart High School in California has one player on each team. Read Article Get Notified
North Florida Christian's Cole Ragans named player of the Year, University Liggett's Dan Cimini is Coach of the Year. Read Article Get Notified
Riley Pint of Aquinas is the Player of the year, Michael Thibodeaux of Teurlings Catholic is Coach of the Year. Read Article Get Notified
Florida edges Texas, California for most all-stars with 12 honorees. Read Article Get Notified
Major League Baseball is back, and a fortunate few high schools across the country have alumni taking the mound on opening day. Read Article Get Notified
Walton, Flanagan, Huntington Beach and Liberty Christian among the favorites to win one of the nation's most prestigious events. Read Article Get Notified
Looking for 2014 info?
Professional photographer Marc Estrada has uploaded a new gallery '2014 Steve Georgiadis Memorial Tournament' containing 301 images. View Pro Photos Get Notified
Tampa Bay Read Full Article
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MaxPreps.com is proud to announce its latest innovation, one that will take every piece of an athlete's high school career and put it in one place. Read Article Get Notified
California leads all states with 71 high school players selected. Read Article Get Notified
Yukon catcher, Manatee outfielder chosen in third round by Red Sox, Phillies Read Article Get Notified
Five high school catchers could go in the first round of the 2013 MLB draft. Read Article Get Notified
AISA A Region 1 league recap: 3/13/13 Read Article Get Notified
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A whole lot of names that you are likely to see in the upcoming Major League Draft. Read Article Get Notified
Looking for 2012 info?


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This Friday's episode of Star Wars: The Clone Wars is a big one. The title, "The Mandalore Plot", gives a clear indication as to why, as the animated series introduces the Mandalorians; a warrior race who are of great interest to many Star Wars fans because of their connection to one of the franchise's most popular characters, Boba Fett.
I had the opportunity to speak to The Clone Wars's supervising director, Dave Filoni, about "The Mandalore Plot", and the multi-episode story arc it kicks off, which also introduces Satine, a woman from Obi-Wan's past who clearly is significant to the famous Jedi.
Filoni and I also discussed what's occurred so far in Season 2, including the darker elements the series has been exploring, from zombies to Anakin's less than heroic side.
To Read More Click Here.


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|Susan Cline <home4...@yahoo.com>
|Re: [VOTE] Reject tally of logo votes
|Thu, 24 Mar 2005 19:32:05 GMT
+1 Reject the tally Kathey Marsden <firstname.lastname@example.com> wrote:It seems to me that it would be very sad and bad karma to have our logo under such a cloud of suspicion. So I would like to call a vote to reject this tally. I've heard lots of great ideas on how to resolve this issue either technologically or socially but I think first we need to establish that this tally is incorrect. Then if we agree to reject, ensuing discussions can determine how to best choose a logo. >> Logo 32 = 20 votes >> Logo 35 = 12 votes >> None of the above = 18 votes > > Vote +1 Reject the tally. New method of choosing a logo is determined by the community. -1 Not to reject the tally. Keep the vote tally as is with 32 as the winner. Thanks Kathey
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Many neurons throughout the rat limbic system discharge in relation to the animal's directional heading with respect to its environment. These so-called head direction (HD) cells exhibit characteristics of persistent neural activity. This article summarizes where HD cells are found, their major properties, and some of the important experiments that have been conducted to elucidate how this signal is generated. The number of HD and angular head velocity cells was estimated for several brain areas involved in the generation of the HD signal, including the postsubiculum, anterior dorsal thalamus, lateral mammillary nuclei and dorsal tegmental nucleus. The HD cell signal has many features in common with what is known about how neural integration is accomplished in the oculomotor system. The nature of the HD cell signal makes it an attractive candidate for using neural network models to elucidate the signal's underlying mechanisms. The conditions that any network model must satisfy in order to accurately represent how the nervous system generates this signal are highlighted and areas where key information is missing are discussed.
Many neurons throughout the classical 'Papez circuit' discharge as a function of an animal's directional heading in the horizontal (or yaw) plane. These neurons are referred to as head direction (HD) cells (Taube et al., 1990a). Each neuron is tuned to a different firing direction and all directional headings are equally represented within a population of these cells. HD cells are quiescent when the animal's head is not pointing in the cells' preferred direction of firing, and then increase their rates of firing linearly as the animal moves its head into the proper orientation. Cell firing is largely unaffected by pitch or roll of the animal's head within ∼90° of the horizontal plane. As long as the animal's head is in a given cell's directional range, cell firing will continue whether the animal is moving or still and is independent of the animal's on-going behavior. There is little adaptation of cell firing when the animal is holding its head in the cell's preferred firing direction (Taube and Muller, 1998).
Fundamental Properties
Each HD cell can be characterized by a number of parameters based on its tuning curve, which is plotted on a firing rate versus head direction graph (Fig. 1A–C). The range of directional headings over which activity is elevated above baseline (background) levels is referred to as the directional firing range. Tuning curves generally have directional firing ranges of 90°, but they can vary from 60° up to 150°. Tuning curves are generally triangular or Gaussian in shape. The peak of the tuning curve is referred to as the peak firing rate of the cell and the animal's HD at the peak is the preferred firing direction of the cell. Peak firing rates vary across different HD cells and range from ∼5 spikes/s to >120 spikes/s. The determinants of a cell's peak firing rate, and the role served by having cells with different characteristic peak firing rates are not known.
The preferred firing direction of a HD cell is controlled by a number of different cues. These cues can come from external or allothetic sources (e.g. visual, auditory, somatic) or internal or idiothetic sources (e.g. vestibular, proprioceptive, motor efference copy). For example, rotation of a salient visual landmark will lead to a corresponding shift in the preferred firing direction of HD cells, indicating that they can be controlled by landmarks (Taube et al., 1990b; Taube, 1995). However, removing the visual cues or turning off the lights does not lead to a change in cell activity although the preferred firing direction may drift after some time (Taube et al., 1990b; Goodridge et al., 1998). Thus, the preferred firing direction of HD cells can be maintained purely via idiothetic information as the animal moves in its environment. Furthermore, firing at the peak rate may continue indefinitely even when the rat remains motionless, with very little adaptation. This combination of characteristics — that HD cells are clearly responsive to external cues and dynamic self-motion information, yet at the same time may continue to fire in the absence of visual or auditory stimulation, motor signals, or vestibular modulation — identifies HD cells as exemplars of persistent neural activity. This article will explore how the persistent activity observed in HD cell firing is generated from known sensory inputs and will raise key issues that remain to be elucidated. For other reviews of HD cell activity see Taube (1998), Sharp et al. (2001a) and Brown et al. (2003). The extent to which HD cell activity is important in spatial and navigational tasks was recently reviewed by Muir and Taube (2002a).
Brain Areas that Contain HD Cells
HD cells were originally discovered in the rat dorsal presubiculum (often referred to as postsubiculum) (Fig. 1A) (Ranck, 1984; Taube et al., 1990a), but have been identified in other brain areas of the classical 'Papez circuit'. These areas include the anterior dorsal thalamic nucleus (ADN) (Fig. 1B), lateral mammillary nuclei (LMN) (Fig. 1C) and retrosplenial cortex (both granular and agranular regions) (Chen et al., 1994; Taube, 1995; Stackman and Taube, 1998; Cho and Sharp, 2001). HD cells have also been identified in significant numbers in the lateral dorsal thalamus and dorsal striatum (Mizumori and Williams, 1993; Wiener, 1993). Other areas where they have been reported in smaller numbers include the medial prestriate cortex, medial precentral frontal cortex, CA1 hippocampus, and the dorsal tegmental nucleus (DTN) (Chen et al., 1994; Guazzelli et al., 2000; Leutgeb et al., 2000; Sharp et al., 2001b). HD cells have been primarily studied in rats, but have also been identified in the ADN of mice and chinchillas (Khabbaz et al., 2000; Muir and Taube, 2002b), and in the presubiculum of monkeys (Robertson et al., 1999). The latter study with monkeys showed that HD cell activity was not dependent on eye movements or where the monkey was directing its gaze. Of the quantitative analyses that have been conducted on HD cells across different brain areas, the tuning curves are remarkably similar, although there are some differences. For example, LMN HD cells tend to have broader directional firing ranges and ADN HD cells tend to have higher peak firing rates. In addition, many LMN cells are modulated by turn direction, that is, they exhibit higher peak firing rates for head turns that pass through the preferred direction in one direction of turn as opposed to the opposite turn direction (Stackman and Taube, 1998).
The percentage of cells that are classified as HD cells varies among different areas. No brain area contains solely HD cells. They are most abundant in the ADN where about 60% of the cells exhibit directional firing (Taube, 1995). The percentage of HD cells in other brain areas are estimated to be as follows: postsubiculum, 25% (Taube et al., 1990a); LMN, 25% (Stackman and Taube, 1998); retrosplenial cortex, 10% (Cho and Sharp, 2001); lateral dorsal thalamus, 30% (Mizumori and Williams, 1993); striatum, 6% (Mizumori et al., 2000). Because the ADN contains such a high percentage of HD cells, it might be interesting to consider how many total HD cells are present within this nucleus. Since each population of ADN HD cells potentially constitutes a complete representation of 360° of space, knowing the absolute number of cells in this population may set useful constraints for modeling how directionally selective networks arise and behave. We therefore estimated the number of cells in the rat ADN by estimating the neuronal density in one coronal brain section stained with thionin at –1.35 mm posterior to bregma. Neurons occupied ∼51.6% of tissue space. We then estimated the total volume of ADN based on the cross-sectional area through seven equally spaced 30 µm sections and calculated the total number of cells based on the average neuronal density. With a total volume of 145.81 (106) µm3 and an average cell volume of 3900 µm3 we estimate that the total number of neurons in the ADN is ∼19 307. If 60% of the cells in this nucleus are classified as HD cells, then there are ∼11 584 total HD cells in the ADN on one side of the brain. While this number should be viewed as a rough estimate, it nonetheless provides a starting point for constructing realistic network models concerned with HD cell discharge. Mulders et al. (1997) estimated the number of cells in layers II/III of the rat presubiculum to be 334 000 and estimated the number of cells in layers V/VI of combined presubiculum + parasubiculum to be 218 000. Using these values, we estimate the total number of cells in the postsubiculum (the dorsal portion of presubiculum) to be ∼227 000 and if 25% of these cells are classified as HD cells, then there are ∼56 750 HD cells in the postsubiculum. Table 1 summarizes these estimates.
Temporal HD Cell Properties
Interestingly, temporal analyses of HD cells in the ADN, LMN, and retrosplenial cortex reveal that firing parameters for cells in these areas are optimized just before the head reaches the cell's preferred firing direction: peak firing rates are higher and directional firing ranges are narrower. Thus, the cell's activity appears to be anticipating where the head will be in the future. For example, for a cell with a preferred firing direction at 45°, cell firing is highest at directions <45° for CCW head turns and >45° for CW head turns. The amount of anticipation is greatest for LMN HD cells (75 ms, Stackman and Taube, 1998; 40 ms, Blair and Sharp, 1998) and ∼25 ms for HD cells in the ADN and retrosplenial cortex (Blair and Sharp, 1995; Taube and Muller, 1998; Cho and Sharp, 2001). In general, HD cells in the postsubiculum neither lag nor anticipate the cell's preferred firing direction. This type of analysis has not been conducted for HD cells in the remaining brain areas where HD cells have been reported. Another analysis that has been conducted for HD cell firing concerns their relationship to angular and linear head velocity. HD cells in the postsubiculum, ADN and LMN discharge at slightly higher rates when the animal moves faster linearly. Similarly, HD cell firing rates in the ADN and LMN, but not in the postsubiculum, are a little higher for faster rotational head turns through the cell's preferred firing direction, although angular head velocity only accounts for ∼1% of the firing rate variance (Taube et al., 1990a; Taube, 1995; Stackman and Taube, 1998; Taube and Muller, 1998).
Generation of the HD Cell Signal
Most work that has investigated how HD cell activity is generated has focused on brain areas within the Papez circuit. Figure 2 shows a mid-sagittal view of a rat brain indicating major areas where HD cells have been identified and the major connections between these areas. Many of these areas are interconnected, which complicates understanding how the signal is generated. However, lesion studies have begun to unravel how the directional signal is processed. Importantly, permanent lesions of the vestibular labyrinth abolish HD cell activity in the ADN (Stackman and Taube, 1997). Similarly, intratympanic injections of tetrodotoxin into the middle ear inactivate the vestibular hair cells for ∼48 h and abolish directional activity in postsubiculum HD cells (Stackman et al., 2002). With both types of lesions, the background activity of HD cells increases compared to pre-lesion controls. In addition, non-HD cells in the ADN are observed to burst periodically. This bursty activity is not observed in intact animals and HD cells in lesioned animals do not become bursty following the lesions. We will return to this point below as it has important implications for models that use attractor networks to simulate HD cell activity. The absence of directional firing is all the more surprising when considering two points: (i) the presence of familiar landmark cues, normal motor/proprioceptive cues, and optic flow are insufficient to generate directional activity, even though HD cells are known to be responsive to these cues (Taube et al., 1990b; Blair and Sharp, 1996; Stackman et al., 2003) and (ii) tonic firing returns to secondary vestibular neurons in the vestibular nuclei, reaching 50% of normal rates within 24 h, and recovering to pre-lesion rates by one week following the labyrinthectomies (Ris and Godaux, 1998). Although it is not clear what mechanisms contribute to the return of the resting discharge rate in vestibular neurons, these observations clearly indicate that the generation of the directional activity is not due to the tonic firing of vestibular neurons.
If an intact vestibular system is essential for establishment of HD firing then lesions of structures in between the vestibular nuclei and postsubiculum should interfere with directional activity in rostrally-projected areas. This notion follows from the observation that, in general, there appears to be a hierarchical processing of information as it flows from the vestibular nuclei to the postsubiculum, making synaptic connections in the nucleus prepositus (nPH) → DTN → LMN → ADN → postsubiculum (see Fig. 2) (Sripanidkulchai and Wyss, 1986; Liu et al., 1984; Shibata, 1987, 1992, 1993a; Allen and Hopkins, 1989; Hayakawa and Zyo, 1990; van Groen and Wyss, 1990, 1995; Wyss and van Groen, 1992). There are also additional pathways that add to the complexity of the circuit. As shown in Figure 2, there is a pathway from ADN → retrosplenial cortex → postsubiculum (Sripanidkulchai and Wyss, 1987; Shibata, 1993b, 1994), and a return pathway from the postsubiculum to LMN (Shibata, 1989; van Groen and Wyss, 1990). Not shown in Figure 2 is a pathway from the DTN → interpeduncular nucleus (both directly and indirectly via the habenular nuclei) → DTN (Contestabile and Flumerfelt, 1981; Groenewegen and van Dijk, 1984; Liu et al., 1984; Groenewegen et al., 1986). Although these other pathways can still be considered a part of the overarching hierarchical scheme, the circuit becomes considerably more complex when considering the presence of reciprocal connections between many of these structures (e.g. DTN and LMN; ADN and postsubiculum; retrosplenial cortex and postsubiculum), as well as descending connections from the postsubiculum to LMN. Importantly, the pathway from DTN → LMN is inhibitory and uses GABA as a neurotransmitter (Gonzalo-Ruiz et al., 1993; Wirtshafter and Stratford, 1993). Commissural projections further complicate the connectivity as crossing fibers connect both the postsubiculum and the DTN to their respective contralateral counterparts, and the LMN sends a significant projection to the contralateral ADN, in addition to its ipsilateral projection. Finally, there is a distinct segregation of connectivity among the subdivisions of the DTN, with the ventral division, or pars centralis, bearing a prominent reciprocal connection with the LMN, and the dorsal division, or pars pericentralis, containing a parallel reciprocity with the interpeduncular nucleus (Hayakawa and Zyo, 1990). Visual information concerning landmarks is believed to originate in secondary visual areas (Oc2M, Oc2L) and projects to the HD cell network either directly to postsubiculum, or indirectly through the retrosplenial cortex (Vogt and Miller, 1983). The directional signal is thought to be conveyed to the hippocampus via postsubicular projections to the superficial layers of entorhinal cortex (Shipley, 1975; van Groen and Wyss, 1990). Taken together, what first appears as a simple circuit is actually a highly complex circuit with many reciprocal connections and side pathways. This situation makes it difficult to decipher how the HD cell signal is processed and what physiological role each brain area serves.
To date, all lesion studies are consistent with this hierarchical processing scheme. Lesions of the ADN abolish directional tuning in the postsubiculum, but not the reverse (Goodridge and Taube, 1997). Bilateral, but not unilateral, lesions of the LMN abolishes HD cell activity in the ADN (Tullman and Taube, 1998; Blair and Sharp, 1999). The primary projections to the LMN originate in the DTN and lesions of this structure abolish directional firing in the ADN (Bassett and Taube, 2001b). Lesions in other brain areas that either contain HD cells, or have intimate connections with ADN, do not abolish the directional signal. Thus, lesions of the hippocampus, lateral dorsal thalamus, or retrosplenial cortex do not disrupt the directional-specific firing of cells in ADN (Golob and Taube, 1997; Golob et al., 1998; Bassett and Taube, 1999). Preliminary studies also indicate that lesions of the posterior parietal cortex do not abolish HD cell activity in ADN (Calton and Taube, 2001). Together with the results from the labyrinthectomies, these lesion studies clearly indicate that subcortical sites are critical for the generation of HD cell activity in limbic system areas.
What types of signals are important for generating HD cell activity? For the most part, HD cells appear confined to rostral areas within the brain including diencephalic and telencephalic structures. But the generation of the directional signal stems from areas within the brainstem that contain cells that are sensitive to the animal's angular head velocity — most notably the DTN and nPH. Except for a few cells that were sensitive to directional heading, the most common neural correlate for DTN cells was angular head velocity, with ∼75% of the cells sensitive to this parameter (Bassett and Taube, 2001a; Sharp et al., 2001b). Bassett and Taube (2001a) observed two different types of angular head velocity cells. One type increased its firing rate proportionately to the speed to which the animal turned its head in either direction — clockwise or counter-clockwise (Fig. 1D). These cells were referred to as symmetric angular head velocity cells and accounted for almost 50% of the total cells in the DTN. The firing rate of the second type was positively correlated to the speed at which the animal turned its head, but only in one turn direction. Turning in the opposite direction led either to no change (Fig. 1F) or a decrease in the cell's activity (Fig. 1E). These cells were referred to as asymmetric angular head velocity cells and composed ∼25% of the DTN population. Most, but not all, asymmetric cells were localized to the hemisphere opposite the preferred turning direction. The firing of about half of the angular head velocity cells, both symmetric and asymmetric, was also modulated by the animal's linear velocity, although no cell's firing rate correlation to linear velocity exceeded its correlation to angular head velocity.
Vestibular nucleus neurons are often classified by their pattern of firing when the head is stationary (Goldberg and Fernández, 1971). Regular firing neurons discharge in a regular, periodic pattern with a fixed interspike interval. In contrast, irregular firing neurons discharge more variably with no definitive peak in the interspike interval histogram. Both symmetric and asymmetric angular head velocity neurons in the DTN were found to contain irregular discharge patterns.
Angular head velocity neurons are also found in the LMN where they constitute ∼43.7% of the cells (Stackman and Taube, 1998; Bassett and Taube, 2001a). Both symmetric and asymmetric cells are found within the LMN (termed 'fast' angular head velocity cells and compose 52.5% of the angular head velocity cells), in addition to a third type of angular head velocity cell, where firing rate is negatively correlated with the speed of head turn for both turn directions. These latter cells are referred to as 'slow' angular head velocity cells and were not observed in the DTN. These slow angular head velocity cells accounted for 47.5% of the angular head velocity cells within LMN. In general, the properties of fast LMN angular head velocity cells are similar to those in the DTN, although the correlation to angular head velocity is not as tight in the LMN compared to the DTN. Furthermore, the slope of the relationship between firing rate and angular head velocity is steeper for DTN than LMN cells. Finally, the firing of ∼10% of the cells in the postsubiculum was correlated to angular head velocity — all the cells were classified as the asymmetric type (Sharp, 1996).
Cell count analyses for LMN and DTN similar to those used above for ADN resulted in a total of 4256 and 1832 cells for each area, respectively. These values indicate that LMN contains ∼1064 HD cells, 979 fast angular head velocity cells, and 881 slow angular head velocity cells. The DTN contains ∼916 symmetric and 458 asymmetric angular head velocity cells. The number of HD cells estimated for LMN compared to ADN — on the order of 1000 versus 10 000 — raises an interesting question: if the directional signal is already generated at the level of the LMN, then what function is served by having a tenfold increase in the number of cells encoding directional heading at the next rostral brain site?
Active versus Passive Motion
Recent studies in the vestibular field show the importance of observing cell firing when an animal is actively moving as opposed to passively turned. Vestibular nucleus neurons discharge in relation to angular head velocity for brief rotations when the animal is passively turned back-and-forth in a sinusoidal manner. Yet, when the animal initiates similar movements voluntarily, neuronal responses are severely attenuated (McCrea et al., 1999; Roy and Cullen, 2001). The response of HD cells to similar passive rotations is more complex. If the animal is restrained tightly by wrapping it in a towel, direction-specific cell firing usually ceases (Taube, 1995). However, if the animal is restrained loosely by holding it in the experimenter's cupped hands, then directional cell firing persists but at a reduced rate (Taube et al., 1990b). Zugaro et al. (2001) reported similar results for animals that were passively rotated on a turntable. If firing of second order vestibular neurons is attenuated during active motion then these vestibular signals would be 'turned off' when the animal is in the freely-moving condition, and one might expect less influence from these neurons than other types of inputs, such as motor or visual cues, during active motion. On the other hand, a paradox arises from the finding that vestibular input is essential for establishing the directional signal.
How these seemingly disparate findings are to be resolved is presently unclear. It is possible that the angular head velocity signals in DTN represent motor and/or proprioceptive information rather than processed vestibular signals. The importance of motor/proprioceptive cues to HD cell discharge has to date been underestimated. Its importance is supported by recent findings showing that vestibular inputs were insufficient to maintain a HD cell's preferred firing direction when the animal was passively transported to a novel environment in the dark —active locomotion between the familiar and novel environments did not lead to this shift in the cell's preferred direction (Stackman et al., 2003). Passive transportation to the novel environment would have activated the vestibular system without normal motor inputs. Other findings supporting a role for motor cues are the anticipatory properties of HD cells discussed above. These properties are more easily accounted for by motor/proprioceptive cues rather than vestibular or other sensory cues. In addition, it is clearly evident that the angular head velocity signals in the DTN have been highly processed because all angular velocity signals in the vestibular nucleus are of the asymmetric type (respond to head turns with increased firing in one direction and decreased firing in the opposite direction) whereas a significant portion of the neurons in the DTN show symmetric characteristics (respond with increased firing in both turn directions). In sum, motor and/or proprioceptive inputs are important contributors to the HD cell signal.
For these reasons it would be interesting to know how angular head velocity signals in the DTN or LMN respond to passive rotations. Would their firing remain robust as in the second order vestibular neurons or would their firing be attenuated similar to HD cells? The one study that addressed this issue examined passive rotations for 12 angular head velocity cells in the DTN and obtained mixed results (Sharp et al., 2001b). Most cells became quiescent or lost their angular head velocity correlate during the passive rotations while only a few cells maintained their angular velocity correlates. These results emphasize the importance of motor cues for many of the DTN cells and provide further support for the notion that motor cues play an integral role in HD cell firing.
Modeling the HD Signal Using Attractor Networks
How angular head velocity signals in the DTN and LMN are processed and transformed into a signal yielding directional heading is one of the central issues in this field. Whether the persistent activity of HD cells arises from intrinsic cellular mechanisms or from network properties that emerge out of a population of these cells is not known. However, because the HD cell signal is so robust, with signal-to-noise ratios frequently over 100:1, it is an ideal signal to model using computational neural networks. Several models have been proposed and although it is beyond the scope of the present review to discuss all of them, each one shares one central feature in common: they all use attractor network dynamics to generate the directional signal (Skaggs et al., 1995; Redish et al., 1996; Sharp et al., 1996; Zhang, 1996; Goodridge and Touretzky, 2000; Xie et al., 2002). This network contains a one-dimensional, continuous ring of HD cells that are interconnected with both excitatory and inhibitory connections. Each HD cell in the ring is tuned to a different directional heading. Cells with overlapping directional firing ranges are linked with excitatory connections, whereas cells with preferred firing directions far apart inhibit one another. This type of network architecture will force neural activity within the network to converge into a 'hill' of excitation that corresponds to one head direction. This hill can then be moved around to different directional headings depending on external influences, such as inputs from vestibular, motor or visual landmark cues.
This type of network architecture is particularly suitable for modeling the HD signal because attractor networks are generally stable and do not require external inputs to maintain their stable state. Instead, the external inputs function to move the hill to a new stable state when the animal turns its head. Attractor networks are also capable of performing a mathematical integration in time. Again, this is an attractive characteristic because starting from a known directional heading, a mathematical integration in time of angular head velocity yields angular head displacement. Perhaps a neural integrator, similar to the one involved in the vestibulo-ocular reflex (VOR), is present in the DTN → LMN pathway and is responsible for generating the HD cell signal. According to this view, the synaptic connections between different HD cells would maintain a stable state when the head is fixed. When the head moves, an angular head velocity signal from either vestibular or motor inputs would be integrated in time by the attractor network and move the activity hill to a new stable state. The amount the hill moves corresponds to the amount the head is displaced which is the integral of the angular head velocity signal. The activity of the hill is sustained (i.e. no adaptation of firing) either through the tonic firing of excitatory afferents in the recurrent network or by the internal membrane properties of the cells. In either case, once the new hill of activity is initiated it is maintained indefinitely until the next perturbation. Attractor network dynamics can also account for the slightly higher firing rates seen for faster head turns in LMN and ADN HD cells (Goodridge and Touretzky, 2000).
While attractor networks are appealing models for generating the HD cell signal they must be able to fulfill several experimental conditions in addition to satisfying the basic firing properties described above:
Removing external inputs will cease direction-specific firing in HD cells in 'downstream' brain areas. This condition follows from the finding that peripheral vestibular lesions abolish HD cell activity in the ADN and postsubiculum (Stackman and Taube, 1997; Stackman et al., 2002). Thus, despite the fact that these vestibular effects are several synapses removed from the ADN, these vestibular lesions have a major impact on HD cell firing such that the activity hill is abolished. Presumably, the HD cell signal is also absent in LMN, although this has never been tested experimentally. Whether an angular head velocity signal is still present in DTN is also unknown. Most attractor networks that have been proposed for generating HD cell activity are designed in a way that removal of external inputs will not disrupt the activity hill. This condition follows from the fact that the hill is derived through local interconnections within a single brain area [or connections across two areas as is the case for the Redish et al. (1996) model] and external inputs are only used to modulate or update the signal by moving the activity hill around. Thus, removal of external inputs will leave the activity hill either (i) stationary, where a subset of the neuronal population will be tonically active; or (ii) unstable such that it will continuously drift. In the latter condition, we would expect HD cells to show periodic bursts of activity. These bursts would occur whenever the activity hill passed through the cell's preferred firing direction and the frequency of the bursts would depend on the rate of drift in the activity hill. Note that in both the stationary and drifting cases, though, the activity hill is sustained. Our findings following peripheral vestibular lesions showed that neither of these predictions was borne out. Of eleven recorded HD cells, none of the cells remained tonically 'on' (i.e. activity hill locked in place). With directional firing ranges of 90°, statistics suggest that we should have observed at least two cells with tonic activity. Moreover, none of the 11 cells showed bursting activity. Bursting activity was observed in the ADN, but it was only seen in cells that were subsequently recorded after the lesion, and the authors attributed the bursting activity to the population of non-HD cells in this area. Importantly, while it is possible to design attractor networks that are dependent on external inputs for generating the activity hill, to date, none of the models that have been proposed for HD cell activity satisfy this requirement.
Attractor networks are frequently characterized as having activity hills that move to new stable states by transitioning through intermediate states that are in between the initial and final states. In other words, if the hill of activity is at 60° and a head turn results in a new directional heading of 150°, then the hill of activity will briefly pass through all the directional headings in between 60 and 150°. The time spent in these intermediate states may be very short, but nonetheless, some activity may be observed in them. However, attractor networks can be designed such that these intermediate states are not mandatory and the activity hill appears to jump from one state to the next. In this scenario, the activity hill at the initial stable state begins to fade as a new hill forms at a different location on the ring attractor (Samsonovich and McNaughton, 1997; Redish, 1999). This latter type of design is more pertinent for HD cells because sensory cue conflict experiments show that HD cells can change their preferred firing directions rapidly without any evidence that intermediate states were activated during the transition (Goodridge and Taube, 1995; Taube and Burton, 1995). Indeed, Zugaro et al. (2003) recently showed that reorientation amongst HD cells can occur as rapidly as 80 ms after a familiar visual landmark appears in the scene.
As discussed above attractor networks usually rely on a set of recurrent excitatory connections within the network to sustain the activity hill in a stable state. They also rely on inhibitory connections to attenuate any activity for cells outside the current directional firing range. This architecture is paramount for the attractor network to function properly. However, the existence of these excitatory and inhibitory connections within the ADN or LMN is not readily apparent in the few anatomical studies that have been conducted on these areas. It is possible, however, that this pattern of connectivity exists, but it is spread over multiple brain areas — in particular, the LMN and DTN. These two areas are attractive candidates because the projection from DTN → LMN is inhibitory while the reciprocal connection is excitatory. Furthermore, larger sized neurons in LMN send projections to both ADN and DTN (Hayakaya and Zyo, 1989), making it easy to imagine LMN HD cells passing directional signals on to their ADN targets while simultaneously inhibiting their out-of-direction neighbors by activating their inhibitory targets in the DTN. Some attractor network models for HD cell activity use two rings of cells (Redish et al., 1996; Xie et al., 2002) or do not rely on recurrent excitatory connections (Rubin et al., 2001).
Visual cues must be able to override control of the preferred direction because most experiments have shown that prominent visual landmarks can control the preferred direction, even when its spatial information conflicts with the on-going spatial information derived from motor and vestibular cues (Goodridge and Taube, 1995; Taube and Burton, 1995; Blair and Sharp, 1996; Zugaro et al., 2000). The model proposed by Skaggs et al. (1995) theoretically showed how visual inputs could override the internal attractor dynamics, although this model was not formally tested. Subsequent models have usually not addressed this issue as they have been more concerned with addressing the internal dynamics of how the activity hill is generated and moved around following head turns (e.g. Redish et al., 1996; Sharp et al., 1996; Zhang, 1996).
In designing a network model that simulates the neural processing between LMN and DTN, the network should contain both symmetric and asymmetric angular head velocity cells in DTN and fast and slow type angular head velocity cells in the LMN. This requirement follows from the relative abundance of these cell types in the two nuclei.
Key Information Needed
There are several areas where key information is needed that would aid understanding of how the HD cell signal is processed. Foremost among these areas is a better understanding of the internal circuitry for each of the brain areas where HD cells are present. Whereas researchers have a good understanding of how the areas containing HD cells are interconnected, little is known about the microcircuitry for these brain areas. Anatomical and electrophysiological techniques are available that could provide important new information. For example, the extent of recurrent excitation or inhibition among individual neurons within a brain region could be determined by using electrophysiological recordings in brain slices. Anatomical techniques could uncover whether the projections from nucleus prepositus → DTN are excitatory or inhibitory. In the future it would be nice to determine how HD cells within one brain area are interconnected with each other as well as to other nearby non-HD cells.
Each of the brain areas where HD cells are present contains many neurons that are not characterized by direction-specific firing. What is the role of these neurons? Are they interconnected with the local HD cells? Are angular head velocity cells within the LMN interconnected with HD cells in this same area? Is the connection only one way or is it reciprocal? Moreover, are all three types of angular head velocity cells within LMN (fast symmetric, fast asymmetric, slow) connected with the HD cells? Which types of DTN angular head velocity cells (symmetric or asymmetric) project to LMN? Finally, what cell types project back to DTN — is it the HD cells or is it angular head velocity cells, and if the latter, which type of angular head velocity cells? It is known that the LMN cells that project to the ADN are the same cells that project back to the DTN (Hayakawa and Zyo, 1989). As one can see, these are all important anatomical questions that must be addressed if researchers want to model the generation of the HD cell signal accurately.
An even more fundamental issue is whether the HD cells in postsubiculum, ADN, and LMN project directly to their principal target regions — namely the entorhinal cortex, postsubiculum and ADN, respectively. While it is assumed that HD cells are the projection cells in these brain areas, there is no direct evidence supporting this notion, and it is quite possible that non-HD cells in these areas are the projection neurons. Simultaneous recording of a HD cell while trying to stimulate it antidromically from a downstream projection area could provide information on this important issue. In addition, as mentioned above, peripheral vestibular lesions abolish the direction-specific activity of HD cells. How these lesions influence the angular head velocity cells in the DTN and LMN is not known. Addressing this issue would provide important information on how HD cell information is processed.
Comparison to the Oculomotor System
Finally, in formulating critical questions for future research on head direction cells, it may help to consider the analogy between the activity of HD cells and that of neurons in another system that has the benefit of many more years of empirical study and modeling. The oculomotor integrator, like the HD cell system, has been identified as an example of persistent neural activity, and has been modeled as a continuous attractor (e.g. Anastasio, 1998; Seung et al., 2000). The two systems share a number of other relevant features, such as some overlapping neural circuitry (i.e. the nucleus prepositus), an interaction between visual and vestibular afference in the case of reflexive (non-saccadic) eye movements, and most importantly, some common computational ends.
Oculomotor integrator neurons have been observed in both mammals (Lopez-Barneo et al., 1982; McFarland and Fuchs, 1992) and fish (Pastor et al., 1994); they discharge linearly as a function of eye position, with higher firing rates reached at more eccentric positions in the orbit. Bursting inputs to the integrator neurons correspond to motor signals that drive movement of the eye, while sustained firing persisting at a constant rate corresponds to the integrated position signal (Robinson, 1989). At this level, there is a clear parallel between the excitatory or inhibitory bursts that drive oculomotor integrator neurons to higher or lower persistent firing rates, and putative bursts of clockwise or counterclockwise vestibular modulation signaling angular head velocity that forces the activity hill around a HD cell ring attractor. This parallel makes clear several critical comparisons between the two systems.
In the oculomotor integrator, a single neuron may vary its firing rate linearly with eye position and will not fire at all below a threshold position. HD cells fire linearly as a function of angular displacement from the preferred firing direction and will cease firing beyond a threshold angle that corresponds with the directional firing range. As with the peak firing rate and the directional firing range of HD cells, the slope of firing rate to position and the positional threshold of oculomotor integrator neurons vary from one neuron to another. A property of oculomotor integrator neurons that is useful for experimental purposes is that they are not perfect; there is a tendency to 'leak' in these imperfect integrators. An animal attempting to hold an eccentric eye position in the dark (thereby having no visual stimuli to direct gaze) will inevitably exhibit a slow drift of the eye back toward a neutral position in the orbit, often referred to as the zero point. This neutral position is determined by the alignment and elasticity of the eye muscles. The drift in eye position toward 'orbit-zero' correlates to a decline in the firing rate of the oculomotor integrator neurons according to a characteristic time constant. As the eye continues to drift, the oculomotor neurons reach quiescence below their positional thresholds.
HD cells, in contrast, do not have a clearly identifiable directional zero. If we are to continue the analogy between the two systems further, then an important question is whether the neural integrator in the HD system is perfect or imperfect. Clearly, the HD cell system does not have the same physical constraints as the oculomotor system, which requires mechanisms to overcome the elastic properties of the eye muscles and the viscous drag of the orbit. Since the HD cell network is not considered a motor system controlling head movement, there is no a priori reason for why the HD cell system could not contain a perfect integrator. On the other hand, if the integrator is imperfect, then how are we to conceptualize leak in the HD cell system? In the oculomotor system, leak corresponds both to a decline in firing rate, and movement of the eye toward zero, and the two are closely correlated because they are causally related. The firing rate of a HD cell and its preferred firing direction do not have such a clear relationship. In fact, if one were to record a declining firing rate from a single HD cell, it would be impossible to distinguish between movement of the activity hill away from the cell's preferred firing direction and decay of activity in the system overall, yet leak in the HD integrator could be conceptualized as taking either of these two forms.
When HD cells are recorded in the dark, the preferred firing directions often drift continuously over several min (Goodridge et al., 1998). This drift in preferred firing direction is reminiscent of the drift of the eye in the dark from an eccentric to a central position , and suggests a failure of an integrator in the HD cell network. Thus, the eventual outcome of leak in the HD cell system might be an activity hill drifting freely with respect to the animal's actual directional heading. To test this hypothesis, we would want to record HD cells in the dark while the animal is immobile, pointing in the direction of a recorded cell's preferred firing direction. If the cell continues to fire indefinitely at its peak rate, then the integrator is perfect. If, over time, the peak firing rate of the cell declined, and the firing rate of a cell with a different preferred firing direction increased, then we could conclude that leak in the HD cell system results in drift of the directional signal (Fig. 3A). But should such a drift be thought of as 'leak'? It could be, from the standpoint of the single HD cell being monitored. In this scenario, after a head turn, the cell loses its activation in the absence of visual or vestibular information. On the other hand, what makes it unlike an oculomotor integrator neuron is that the activation is preserved elsewhere in the network, so as the firing rate declines in one cell, it must increase in another by virtue of the network connectivity. The 'zero point', then, would correspond to a state of constant instability of the activity hill, driven simply by the aggregation of small asymmetries in the velocity input while the head is motionless, rather like an eye suddenly cut free from the ocular muscles and left to drift in the socket. Furthermore, drift of the activity hill would imply that the persistent activity observed in HD cells is attributable primarily to the internal connectivity of the HD network, rather than depending upon extrinsic excitation, since some signal would persist even with no afferent input.
Alternatively, if in the same scenario directional firing failed over time in one HD cell without a corresponding increase in firing elsewhere in the HD network, then leak would be evident as a decrease in the firing rate of the cell towards its baseline firing rate, without a shift of the activity peak, implying an overall loss of activity in the network (Fig. 3B). This finding would show that persistent activity depends upon either intrinsic membrane properties of the HD cells, or excitatory input originating outside the system. Some models of oculomotor integration employ three mechanisms to account for the persistent neural activity: (i) saccadic bursts, originating outside the attractor network that drive the integrator signal from zero; (ii) a cellular time constant intrinsic to the integrator neurons; and (iii) the network connections that prolong the cellular time constant (Anastasio, 1998; Seung et al., 2000). Unless we define a zero for HD cells that corresponds to the central position in the oculomotor integrator, from which a time constant of decay can be derived, the relative contribution of each mechanism is untestable using the methods employed for investigating the oculomotor integrator. Although firing rate adaptation has been examined over relatively short time periods (Taube and Muller, 1998), the experiment described above for holding the head still over long periods remains to be done, and the previously described effects of restraint may make it difficult to execute. Unpublished observations, however, suggest a time constant for HD cells orders of magnitude longer than those for oculomotor integrator or vestibular neurons.
The results from vestibular lesion studies imply that the role of the vestibular system goes beyond moving the hill of activity around the network. It indicates that the vestibular system is particularly involved in driving the generation and persistence of the HD cell signal. If this situation is true, then a HD cell firing constantly in its preferred firing direction following a head turn may be seen as the integration of the velocity signal that corresponds to the head turn, just as the position-related firing of the oculomotor integrator neuron represents the integration of the velocity-related saccadic burst that moved the eye to its new position. It should be noted that when a rat is motionless and the head is at zero angular velocity, there is still a strong signal that could feed forward onto the HD cell network because of the tonic high firing rates in neurons within the vestibular nuclei. This condition is in contrast to the situation following labyrinthectomies when the activity hill in the attractor network has permanently broken down despite the eventual recovery of tonic firing rates within the vestibular nuclei (Stackman and Taube, 1997; Ris and Godaux, 1998).
Oculomotor integrator neurons continue to fire while holding the eye in an eccentric position, but some authors have postulated another type of integrator that resets to zero at the completion of each saccade (Jurgens et al., 1981; Kustov and Robinson, 1995). In these models, a velocity-to-displacement integration occurs, but the eye displacement signal resets to zero immediately after each saccade by a rapid leak, so that the next saccade can be coded in terms of displacement from the current position. If an updated directional signal following a head turn is the result of an integration of angular velocity over time, then the HD cell system may also be comparable to the resettable displacement integrator in models of saccadic eye movements. Thus, each stable head position becomes a relative zero point to which the next integrated displacement is added when the head turns. In the light, resetting may be caused or facilitated by visual feedback from the environment. In the dark, the successive addition of displacement values without visual feedback may be responsible for the accumulation of error and observed as the preferred firing direction drifting in the dark. This suggestion is intriguing because it implies that a memory of the previous head direction is briefly preserved in the network, and is compared to a representation of desired head direction, an idea that is notable in light of the anticipatory firing properties of HD cells in the LMN and ADN (Blair and Sharp, 1995; Taube and Muller, 1998). As a measurable phenomenon, leak in this case would be altogether different than in our previous comparison and would not be evident in the firing activity of an isolated HD cell. In our postulated experiment described above, if the head were fixed in the dark after a single head turn, we would expect the HD integrator to reset to zero at the new direction and an external perturbation of the system would be required to elicit a drift of the activity hill back toward the original head direction. Such a finding would serve as indirect evidence of an incompletely reset displacement signal.
In addition to the oculomotor integrator and the resettable integrator of the saccade system, there is another example of a neural integrator that prolongs a velocity signal, in this case one for the angular velocity of head turns. Within the brainstem circuits that mediate vestibular, vestibulo-ocular, and optokinetic reflexes, vestibular signals outlast the afferent signals in the VIIIth nerve. The longer time constant for the decay rate of vestibular signals in secondary vestibular neurons and other brainstem areas, including the nucleus prepositus, is referred to as velocity storage. This process is thought to play an important role in improving the VOR at low frequency (long duration) head turns and also functions to realign the eye movement axes with the direction of the current gravito-inertial acceleration of the organism (Leigh and Zee, 1999). There is also evidence that the vestibular signal subserving the subjective experience of angular velocity is affected by velocity storage (Okada et al., 1999). Thus, one might wonder whether this mechanism makes a similar contribution to the HD cell signal, improving the accuracy of updated heading during low frequency head turns. Experimental manipulations of the velocity storage integrator may produce measurable effects on HD cell activity.
This article has summarized the major properties of HD cell activity. The strength of this signal and the ability to measure it accurately provide an ideal system for understanding how the nervous system processes raw sensory information and transforms it into a high level cognitive signal that encodes the animal's perception of its directional heading in allocentric space. The nature of the HD cell makes it an attractive candidate for using neural network models to elucidate the underlying mechanisms.
This research was supported by grants from the National Institute of Mental Health (MH48924, MH01286) and the National Aeronautics and Space Administration through the NASA Cooperative Agreement NCC 9–58 with the National Space Biomedical Research Institute. We thank David Zee for helpful comments on portions of this manuscript.
|Brain area
|Total cell number
|Percentage of HD cells
|Percentage of AHV cells
|Number of HD cells
|Number of AHV cells
|Dorsal tegmental nucleus (DTN)
|Bassett and Taube (2001a)
|Sharp et al. (2001b)
|Lateral mammillary nuclei (LMN)
|Stackman and Taube (1998)
|Anterior dorsal thalamus (ADN)
|19 300
|11 600
|Taube (1995)
|Postsubiculum (PoS)
|227 0001
|56 750
|22 700
|1Mulders et al. (1997)
|2Taube et al. (1990b)
|3Sharp (1996)
|Brain area
|Total cell number
|Percentage of HD cells
|Percentage of AHV cells
|Number of HD cells
|Number of AHV cells
|Dorsal tegmental nucleus (DTN)
|Bassett and Taube (2001a)
|Sharp et al. (2001b)
|Lateral mammillary nuclei (LMN)
|Stackman and Taube (1998)
|Anterior dorsal thalamus (ADN)
|19 300
|11 600
|Taube (1995)
|Postsubiculum (PoS)
|227 0001
|56 750
|22 700
|1Mulders et al. (1997)
|2Taube et al. (1990b)
|3Sharp (1996)
aBassett and Taube (2001) did not report any 'classic' HD cells in the DTN, whereas Sharp et al. (2001b) reported a small number.


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Patients with diffuse large B-cell lymphoma of germinal center origin with BCL2 translocations have poor outcome, irrespective of MYC status
- Affiliations:
1 The Faculty of Medicine, Aalborg University, VBN
2 Aalborg University Hospital, The Faculty of Medicine, Aalborg University, VBN
3 Klinik Medicin, The Faculty of Medicine, Aalborg University, VBN
4 Blodsygdomme (Hæmatologi), The Faculty of Medicine, Aalborg University, VBN
5 Department of Hematopathology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
6 unknown
7 Roche Molecular Systems
8 Department of Hematology, San Bortolo Hospital.
9 University of Louisville School of Medicine
10 Hospital Universitario Marques de Valdecilla
11 Department of Clinical Medicine, The Faculty of Medicine, Aalborg University, VBN
12 Memorial Sloan-Kettering Cancer Center
13 Department of Pathology, Weill Medical College of Cornell University, New York, NY, USA.
14 The Methodist Hospital, Houston, TX, USA
15 Columbia University Medical Center
16 University of California School of Medicine, San Diego, CA, USA,
17 University of North Carolina School of Medicine, Chapel Hill, NC, USA
18 Cleveland Clinic Foundation
19 University of Maryland School of Medicine, Baltimore, MD, USA,
20 Department of Pathology, University of Hong Kong Li Ka Shing Faculty of Medicine, Hong Kong, China.
21 Zhejiang University School of Medicine
22 Radboud University Nijmegen Medical Centre
23 City of Hope National Medical Center
24 University of California San Francisco School of Medicine
25 San Raffaele H. Scientific Institute
26 University of Wisconsin Hospital and Clinics
27 Department of Hematology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
28 Department of Hematology, Gundersen Lutheran Health System, La Crosse, WI, USA.
29 Odense Universitetshospital
30 Hospital Universitario Marques de Valdecilla
31 Memorial Sloan-Kettering Cancer Center
32 Cleveland Clinic Foundation
- Subtitle:
- A report from an international DLBCL rituximab-CHOP consortium program study
- 10.3324/haematol.2012.066209
- Type:
- Journal article
- Language:
- English
- Published in:
- Haematologica, 2013, Vol 98, Issue 2, p. 255-263
- Main Research Area:
- Medical science
- Publication Status:
- Published
- Review type:
- Peer Review
- Submission year:
- 2013
- Scientific Level:
- Scientific
- 235518389


text:
On the development of an innovative gas-fired heating appliance based on a zeolite-water adsorption heat pump; System description and seasonal gas utilization efficiency
Dawoud B.,Viessmann Werke Allendorf GmbH
Applied Thermal Engineering | Year: 2014
The main objective of this work is to introduce an innovative hybrid heating appliance incorporating a gas condensing boiler and a zeolite-water adsorption heat pump. The condensing boiler is applied to drive the zeolite-water heat pump for the heating base-load and to assist the heat pump in the so called "mixed operation" mode, in which both the heat pump and the condensing boiler are working in series to cover medium heating demands. Peak heating demands are covered by the condensing boiler in the so called "direct heating" mode. The three operation modes of the hybrid heating appliance have been technically described. In addition, the laboratory test conditions for estimating the seasonal heating performance according to the German Guideline VDI 4650-2 have been introduced. For both heating systems 35/28 °C and 55/45 °C, which represent the typical operating conditions of floor and high temperature radiating heating systems in Europe, seasonal heating gas utilization efficiencies of 1.34 and 1.26 have been measured, respectively with a ground heat source. In two field test installations in one-family houses in Germany, the introduced heating appliance showed 27% more seasonal gas utilization efficiency for heating and domestic hot water production, which is equivalent to a CO2-emission reduction of 20% compared to the gas condensing boiler technology. © 2014 Elsevier Ltd. All rights reserved. Source
Dawoud B.,Viessmann Werke Allendorf GmbH
Applied Thermal Engineering | Year: 2013
A possibility to enhance both heat and mass transfer characteristics of an adsorber heat exchanger is to apply the adsorbent directly to its surface in form of a consolidated layer. As the majority of the available publications on the effect of both coating technology and adsorbent layer thickness on the adsorption kinetics deals with small scale adsorbent samples, the results obtained can only represent the best case design of an adsorber heat exchanger. This article presents, therefore, a comparison between the adsorption kinetics of water vapour on small as well as two different full scale coated adsorber heat exchanger types with AQSOA-Z02 layers of Mitsubishi Plastics Incorporation under quasi isobaric conditions of adsorption heat pumps. The small scale coated samples have a zeolite dry mass of 200 mg and layer thicknesses of 200, 300 and 500 μm while the full scale adsorbers have a coated zeolite mass between 1.5 and 2.5 kg and layer thicknesses of 150, 200, 300, 400 and 500 μm. In the investigated adsorption heat pump module, up to 52.7 and 57.3% of the equilibrium differential water loading measured with the small scale coated substrates have been obtained after an adsorption-evaporation times of 300 and 600 s, respectively. © 2012 Published by Elsevier Ltd. Source
Self-calibrating combustion controller - The proven response to the challenges posed by future gas qualities [Selbstkalibrierende Verbrennungs-regelung - Die bewährte Antwort auf Herausforderungen durch künftige Gasqualitäten]
Dzubiella M.,Viessmann Werke Allendorf GmbH
GWF, Gas - Erdgas | Year: 2011
In its endeavours to safeguard the long-term supply of natural gas, the German gas industry draws on fuel from different sources. In addition, an increasing proportion of alternative gases, such as LNG, EASEE gas and bio-enriched natural gas will be fed into the supply networks. The resulting wide range of gas qualities can only be accommodated by gas condensing boilers equipped with conventional air-gas mixers with some considerable conversion effort. Our response to this challenge is the self-calibrating Lambda Pro Control combustion controller. It makes all combustion-related adjustments of the appliance during commissioning as well as any manual alteration in the case of changes in the gas quality unnecessary. Since its launch in 2005, the Lambda Pro Control has proven its capability in more than 500.000 gas condensing boilers, with excellent results. Source
On the effective thermal conductivity of wetted zeolite under the working conditions of an adsorption chiller
Dawoud B.,Viessmann Werke Allendorf GmbH |
Sohel M.I.,University of Canterbury |
Freni A.,CNR Institute of Neuroscience |
Vasta S.,CNR Institute of Neuroscience |
Restuccia G.,CNR Institute of Neuroscience
Applied Thermal Engineering | Year: 2011
This paper presents a theoretical model for predicting the effective thermal conductivity of wetted zeolite. The model comprises the thermal conductivities of the zeolite crystal as well as of the adsorbed water. The temperature dependence of both thermal conductivities is considered. Moreover, the contribution to the effective thermal conductivity due to vapor conductance is also taken into account. The effective thermal conductivity of 4A zeolite-water is measured by transient "hot wire" method under various conditions of vapor pressure, temperature and water loading. The measurement ranges are chosen according to the operating conditions of a typical adsorption cooling cycle. The experimentally measured data are fitted to the proposed theoretical model. The maximum deviation between the experimental results and the theoretical values is estimated to be ±5.8%. The validated model is used to realize a zeolite 4A conductivity chart, which represents an useful tool for thermal design of adsorption machines. © 2011 Elsevier Ltd. All rights reserved. Source
Adsorbent coatings for heat pumping applications: Verification of hydrothermal and mechanical stabilities
Freni A.,CNR Institute of Advanced Energy Technologies Nicola Giordano |
Frazzica A.,CNR Institute of Advanced Energy Technologies Nicola Giordano |
Dawoud B.,Viessmann Werke Allendorf GmbH |
Chmielewski S.,Viessmann Werke Allendorf GmbH |
And 2 more authors.
Applied Thermal Engineering | Year: 2013
This paper presents novel experimental methods for verification of both hydrothermal and mechanical stabilities of adsorbent coatings. Experiments have been carried out on zeolite-based coatings over aluminum substrates, prepared by a dip-coating technique developed at CNR-ITAE. Hydrothermal aging of several adsorbent coatings is ongoing. Adsorption and structural stability of some samples under test was successfully verified after 35000 aging cycles by isobars measurement and XRD analysis. Mechanical properties of coatings have been evaluated by applying different typologies of static and dynamic mechanical stresses. Results obtained have been compared with those achieved by subjecting adsorbent coatings prepared by Mitsubishi Plastic Incorporation (MPI) to the same characterization protocol. The comparison between the two types of coating returned that MPI coatings posses similar thermal stability and better mechanical strength than CNR-ITAE coatings. © 2012 Published by Elsevier Ltd. Source


text:
Williams & Smtihells Ltd - Sweden Yacht 38. Peter Norlin designed, Quality built, fast, blue water cruiser, with classic lines and great accommodation. Adaptable for long distance sailing, live-aboard cruising or even coastal/med explorations. Volvo Penta 28hp installed 1984, Teak laid on GRP decks, Surveyed 2014 (report available on request), Lewmar winches, full sail wardrobe, Sleeps 6 in 3 cabins plus 2 in saloon. £57,000
Aft Cockpit
White, GRP hull
Teak on GRP deck relaid 2010
GRP Superstructure
Lead, fin keel
Spade rudder
Rudder bearing replaced 2006
Wheel Steering
Steering cables replaced 2006
Last Osmosis Treatment :11/07/2007
Last Structural Survey: 27/10/2014 (available on request)
Volvo 28HP engine (1984)
Engine head rebuilt 2010
New heat exchanger
Saildrive rebuilt 2010
3 Bladed Gori propeller
3 x Exide 96Amp/h domestic batteries (New in June 2016)
Exide 74Amp/h engine starter battery (New in June 2016)
High output alternator linked to smart charge system' serviced 2016
Mastervolt shore power system
Charging via Shore/ Engine
100ltrs Steel fuel tank
2 x 320ltrs (total) Steel water tanks
Selden spar, boom and spinnaker pole
Stainless steel standing rigging
Both standing and running rigging replaced 2010
Spinnaker: Seldon pole
2 x Lewmar 48 genoa sheet winches
2 x Lewmar 48 spinnaker sheet winches
4 Lewmar 40 halyards winches
Lewmar 30 main winch
White, Hood, slab reefed fully battened mainsail (2010)
White, Hood, furling genoa
White, furling jib/staysail (2010)
Blue/white , snuffer spinnaker
White storm jib
Sleeps 8 in 3 cabins
2 x Doubles plus 2 x singles plus 2 x saloon berths
Mahogany interior joinery
Ardic heater fitted 2003, unused
Head with shower
Mobilife cooker
2 x Hobs
Steel sink
Ice maker
Cutlery & Crockery
Cooking Utensils
Pots and Pans
35lb CQR anchor with 55m 10mm chain
Electric Windlass
Windlass and chain replaced 2011
5 x Fenders
Boat hook
Swimming ladder
Boarding ladder
Deck shower
Spray Hood Bimini
Nav Lights
ST60+ Speed log
ST60+ Wind indicator
ST60+ Echosounder
Raymarine Autohelm replaced 2010
Raychart 620 plotter (GPS included)
Raytheon SL70 radar
Standard Horizon VHF
6man Viking Liferaft (new in 2010)
Electric bilge pump
Manual bilge pump
Grab Bag
Emergency Tiller
(The condition or level of safety equipment on board is not to be negotiated on following survey. It is likely to be listed by most surveyors but is not structural or an integral working part of the vessel and is not to be used to further negotiate the price down after survey. We strongly suggest that for your own personal safety that when purchasing a yacht you provide new safety equipment rather than relying on second hand gear.)
Zodiac 310 Fastroller tender
Tohatsu 10HP outboard engine
Last serviced 2015/2016
The Company offers the details of this vessel in good faith, in this case we are acting as Brokers only. Whilst every care has been taken in their preparation, the correctness of these particulars is not guaranteed. The particulars are intended only as a guide and they do not constitute a term of any contract. A prospective buyer is strongly advised to check the particulars and where appropriate at his own expense to employ a qualified Marine Surveyor to carry out a survey and/or to have an engine trial conducted which if conducted by us shall not imply any liability for such engine on our part. This vessel is offered subject to prior sale, price change, or withdrawal without notice.
Trusted British Yacht Brokers, Established almost 40 years, specialising in Cruising and Blue Water yachts permanent offices in Lefkas Marina, Ionian Greece & Portsmouth, UK. We specialise in live aboard blue water cruisers. Experienced, Professional, Qualified All Brokers are Full Members of ABYA, we work to a code of practice with safe Clients bank Accounts and carry PI Insurance. As Agents for Allures Yachting we represent a respected brand of blue water cruiser with Aluminium hulls, GRP topsides and Lifting keels. Experience our Service we sell yachts nothing else. Call us for a chat 00 44 (0)1329 827053
|Sales status:
|Sweden Yachts
|Year built:
|Length (m):
|28.0 hp
|Max Draft
|12.5 feet
|Waterline length
|31.17 feet
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