In this section we look at two possibilities. The first is that damage to a component of the cognitive memory system results in a disconnection of retrieval mechanisms from storage. The components of the cognitive memory system include medial temporal lobe, medial thalamus, mamillary bodies, basal forebrain cholinergic system and orbital prefrontal lobe. Damage to any of these can produce amnesia. The frontal lobe is theorized to control retrieval processes while the other areas control storage of information.
Amnesia results from loss of access rather than loss of stored information.
Warrington and Weiskrantz reached this conclusion by reviewing the pattern of difficulties exhibited by amnesics in laboratory tests of their memory. Another theory is that amnesia represents a loss of ability to store or retrieve the context in which the contents of a memory were experienced. On a memory test the subjects were first asked to discriminate the day 2 pictures from day 1. Normal subjects did this almost perfectly, showing that they had excellent memory for the context in which pictures had been viewed. The amnesic patients were quite poor at this discrimination task, yet performed equally to the normals on a modified test in which they were asked whether test pictures from bith days were familiar.