the memory engram Flashcards
History
Gall: the history of localization of brain function, as he was the first to suggest that personality traits may somehow relate to bumps/ areas on the head.
Broca: patients with specific deficits found to have damage to specific areas
karl Lashley: tried for years to discover which part of the brain was responsible for memory.
Trained rats on a maze to find food, leision different parts of brain to see effect on memory- didnt see any
came up with two principles:
1. Mass action - complex aspects of memory are observed by entire cortex
2. equipotentiality- if you remove one part of the cortex other parts work to support the function you removed
(criticism)
Von bechterew - first clue that memory is supported by certain brain structures.
Physician who noted patients with memory problems suffered a softening and deterioration of the temporal lobe
Definitive evidence supporting distinct memory circuit in the brain
H.M operated on for seizures caused by a crash on his bike.
- removed medial temporal lobe - seizure epicenter.
- most of hippocampus was removed
Results
- From the moment of the surgery onwards he could form no new memories (antregrade) episodic memory
In addition to this he also suffered temporally graded RETROGRADE amnesia = memories just before surgery impaired but the further back you go the more he could remember
However his WORKING MEMORY remained in tact
- normal digit span
- Wickelgren rate of forgetting was normal
- UNLESS he was interrupted (required constant rehearsal)
Exept for is VISUAL working memory, which was impaired.
Presented elipse, then presented many different ones, couldn’t distinguish.
Encoding visual and spatial properties were restricted
Could perform motor learning task (mirror drawing)
- working procedural memory
- he is able to learn in the long term
- could not remember the autobiographical information (issues with declarative memory)
Declarative vs Procedural (squire)
Procedural memory: riding a bike, playing guitar
Declarative memory (facts)
- Episodic memory: Your birthday (what, where, when)
- Semantic memory: definitions, your mum’s birthday
Mishkin
HM, big leision, where exactly is the memory engram?
- struggled with recognition
- Showed monkey familiar vs novel objects, if the monkey could recognize the old object and displace the new one they would be rewarded.
- Removed hippocampus and surrounding areas
Findings:
Monkeys recognition memory was not profoundly affected by removal of just the hippocampus but removal of surrounding areas such as HM showed a notable deficit in recognition memory.
= highlighting sub part of the temporal lobe which is responsible for specific kinds of memory= recognition memory
Perirhinal cortex vs hippocampus
Damage to this cotex as found in monkeys results in impairments of recognition memory
Nemanic et al found that when using the tendency of rats to investigate novel items, rats with hippocampal lesions performed just as well as controls, however animals with only perirhinal regions performed much worse.
The hippocampus however was seen to greatly effect the performance of rats during spatial recognition tasks
Hippocampus: object recognition
perirhinal cortex: spatial recognition
FMRI role of spatial and episodic memory
FMRI shows activation of the hippocampus when navigating a simulated spatial scene
Evolution and the hippocampus
Sherry and Duff
Food storing birds were found to have larger hippocampi than other birds
Also evident in humans (mcguire)
taxi drivers were found to have larger posterior area of the hippocampus than bus drivers
The anterior part was found to be smaller.
This is an example of brain change due to experience and neural plasticity
They were given other kinds of tasks
- performance of taxi drivers was always better on spatial awareness tasks
-rey-osterith figure task found that taxi drivers were impaired relative to bus drivers.
This reflects structure of hippocampus?
There are also SUBCORTICAL areas involved in memory
Papez circuit : hippocampus is a part of it
James papez identified that damage to the mamillary bodies and the anterior thalamus causes memory deficits/ an amnesia
Not only one part that affects memory but many interact
Conclusions
Lashley was mostly wrong, there are localized areas that are involved in brain function.
- medial temporal lobe is vital in memory function
- distinction between procedural and declarative memory
- perirhinal cortex = responsible for object recognition
- hippocampus = important in spatial memory, navigation and episodic memory
- hippocampus part of pepez circuit
