What is In which of the following chronic Conditions, degenerative changes in the brain are Seen which are not a pa of normal ageing? and explain in detail?
Amnesia is a deficit in memory caused by brain damage or disease, but it can also be caused temporarily by the use of various sedatives and hypnotic drugs. The memory can be either wholly or paially lost due to the extent of damage that was caused.There are two main types of amnesia: retrograde amnesia and anterograde amnesia. Retrograde amnesia is the inability to retrieve information that was acquired before a paicular date, usually the date of an accident or operation.In some cases the memory loss can extend back decades, while in others the person may lose only a few months of memory. Anterograde amnesia is the inability to transfer new information from the sho-term store into the long-term store. People with this type of amnesia cannot remember things for long periods of time. These two types are not mutually exclusive; both can occur simultaneously People with amnesia can learn new information, paicularly non-declarative knowledge. However, some people with dense anterograde amnesia do not remember the episodes during which they previously learned or observed the information. Declarative information Some patients with anterograde amnesia can still acquire some semantic information, even though it might be more difficult and might remain rather unrelated to more general knowledge. H.M. could accurately draw a floor plan of the home in which he lived after surgery, even though he had not lived there in years. The reason patients could not form new episodic memories is likely because the CA1 region of the hippocampus was a lesion, and thus the hippocampus could not make connections to the coex. After an ischemic episode following surgery, an MRI of patient R.B. showed his hippocampus to be intact except for a specific lesion restricted to the CA1 pyramidal cells. Non-declarative information Some retrograde and anterograde amnesics are capable of non-declarative memory, including implicit learning and procedural learning. For example, some patients show improvement on the pseudorandom sequences experiment as healthy people do. Therefore, procedural learning can proceed independently of the brain system required for declarative memory. According to fMRI studies, the acquisition of procedural memories activates the basal ganglia, the premotor coex and the supplementary motor area, regions which are not normally associated with the formation of declarative memories. This type of dissociation between declarative and procedural memory can also be found in patients with diencephalic amnesia such as Korsakoff's syndrome. Another example demonstrated by some patients, such as K.C. and H.M, who have medial temporal damage and anterograde amnesia, still have perceptual priming. Those patients did well in the word fragment completion test. Ref Harrison20th edition pg 2134