link between top-down (bottom-up) processing and cortex layers What are the relations between top-down and bottom-up processings and the flows of information in the brain? For example, does top-down processing start from some layers and go to lower layers? 
If so does the information remain in the same area of the brain or can it travel from a layer of one area down to lower layers of an others areas? 
Also how are feedforward (feedback) pathways related to bottom-up (top-down)?
It is generally thought that thalamic input comes in layer 4, feed back from higher areas come through layer 1 to layer 2/3 and feed forward is sent from the deeper layers.  

see Canonical Microcircuits for Predictive Coding
Andre Bastos, W. Martin Usrey, Rick Adams, George Mangun, Pascal Fries, and Karl Friston
http://psych.nyu.edu/clash/poeppellab/JournalClubPapers/BastosFristonNeuron12.pdf

who cite Douglas, R.J., and Martin, K.A. (1991). A functional microcircuit for cat visual cortex. J. Physiol. 440, 735–769.