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Visual Memory Deficit Amnesia The hippocampus is intitially crucial for storage + recovery of memory trace - but their contribution diminishes as consolidations proceeds The association cortex from different senses become bound together - form a link + no longer necessary to use hippocampusAll these cortical areas cascade information from one another if one is triggered Greenberg & Rubin (2003) - burger example
- Smell of burgers leads to activation in olfactory cortex
- This via MTL mediation would activate a pattern of firing in visual cortex that represents the memory of a friend once cooking them
- This activity in visual cortex - may stimulate new activity in audiotry cortex - represents the sound of a conversation once had with that friend
? This is the CASCADE of activation
- This activity would also stimulate regions dedicated to language, narrative + emotion - impart the emotional tone to the memory
? The recall of an autobiographical memory occurs over one measurable time period - but not in one brain location => it is located in time - but distributed in space. Rubin & Greenwood (1998) ?When an autobiographical memory is recalled info in widely separated areas of cortex are excited :
- E.g. a familiar sound may lead to activation in auditory cortex - which either directly or via the hippocampal mediation might activate a pattern of firing in visual cortex - stimulating a visual image
- This activity in visual cortex may in turn stimulate new activity in visual, auditory + other cortices - stimulating visual images, sounds, smells - while feed-backing to the original pattern of firing in auditory cortex ? cascade of activation - produces a patterns of firing similar to that present during the original experience
Most memories have strong visual component:
? Crawley & Eacott (2006)
- Asked to recollect + describe a memory from childhood ? investigated the extent to which the memory had visual, auditory, spatial etc aspects
- Visual detail is the largest + most regularly reported detail - this is higher than any other sensory component
? Suggestive that memories rely heavily on visual representations
? Rubin (2006)
- Participants are given a cue word - asked to retrieve and episodic memory associated with that word whislt undergoing fMRI
- Asked to hit a button once memory brought to mind
- Large activation of the hippocampus at memory retrieval, PFC activated when making a decision on the memory to think of
- Visual cortex was v. active - retrieval of the memory activated the visual cortex
? Further suggests there is a large amount of visual info in memory representations What happens to EM if visual association cortex is damaged?
New experiences will have a degraded visual component and so anterograde memories will be formed with this degraded input. Relative absence of visual component will affect but may not be devastating to memory integrity.
Pre-existing memories (i.e. retrograde) were formed of events that included an intact visual component. Stored visual component will be degraded/lost.
For retrograde memories the lack of visual component may also prevent the cascade of associations to other modality components, affecting retrieval of them too. This will effect all retrograde memories equally, so there will be no temporal gradient to retrograde amnesia.
Hypothesis: the loss of visual association cortex will result in a form of amnesia with the above characteristics. Called Visual Memory Deficit Amnesia (VMDA)
Differences between MTL amnesia
Differences between VMDA + cortical/retinal blindness
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