Week 10 - Memory

The nature of memory (the fact that it is a 'process' rather than an entity or ‘thing’) makes it difficult to localise to a specific area in the brain.  Further, memory involves several procedural components (including encoding, recall, recognition and retrieval) as well as different modalities (auditory, visual and olfactory).  However, evidence has shown that certain areas of the brain are activated (and therefore associated with) particular parts of this process in the healthy brain. Damage to these regions can lead to deficits in some types of memory (Martin, 2006).
 
The hippocampus is understood to play a part in the consolidation of declarative long-term memory and spatial navigation.  Hippocampal damage has been shown to result in anterograde amnesia – difficulty in forming new memories subsequent to damage - although ‘old’ memories can remain largely intact.  Investigating the distinct role of the hippocampus, Teng and Squire (1999) highlight the case of patient E.P.
   

Patient E.P suffered severe amnesia following a bout of encephalitis which caused near complete damage to all components of his medial temporal lobe, including the hippocampus.  He had profound difficulty recognising people he regularly came into contact with, could only perform at chance level in both verbal and non-verbal recognition memory tasks and had extremely poor recollection of events and facts during the 40 years prior to his encephalitis.  In a series of topographical memory tests, E.P was asked to recall the spatial layout of the neighbourhood he grew up in some 50 years earlier.  E.P performed well, demonstrating “intact memory for remote autobiographical episodes...and intact memory for remote spatial information” (Teng & Squire, 1991, p.676).  Remarkably, despite the fact that E.P could remember the layout and features of a place he had moved away from some 50 years earlier, E.P could not recognise or navigate his way around his current neighbourhood. 

 

Teng and Squire (1999) posit that their own findings concur with evidence in the literature which assigns the medial temporal lobe an essential role in the formation of spatial and non-spatial long-term declarative memory  “but not for the retrieval of very remote spatial or non-spatial memories” (p.676).  

Episode of Scientific American Frontiers featuring Patient E.P

References
Teng, E. & Squire, L. R. (1999). Memory for places learned long ago is intact after hippocampal damage.Nature, 400, 675-677

Martin, G. N. (2006).  Memory. In Human Neuropsychology (2nd ed.). Essex: Pearson Education Ltd