The brains response to experience
- Communication of cells through synapses
- Learning - experience changes cells
- Memory - how changes strengthen connections between cells
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Bilateral Medical Temporal Lobectomy
- H.M. was an epileptic who, in 1953, has his medial temporal lobes removed.
- His seizures were dramatically reduced - but so was his memory.
- Mild retrograde amnesia and severe anterograde amnesia.
- Types of memory problems were show by which bits of brain were retained.
- Retrograde: Unable to remember the past (backwards acting)
- Anterograde: Unable to form new memories.
- While HM was unable to form most types of new, long-term memories, his STM was intact.
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- Digit span - HM could repeat digits as long as the time between learning and recall was within the duration of STM (Add numbers and repeat).
- Block-tapping memory-span test: This test demonstrated that H.M's amnesia was global - not limited to one sensory modality. (Squarelights come and go and you have to tap them and remember order and location).
- Mirror drawing task - H.M exhibited improvement with practice. He was able to show memory for skills - demonstrating that he can learn also demonstrated by performance of the rotary-pursuit and a drawing task, although he was not aware of learning.
- HM readily 'learned' responses.
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Contributions of HM's case
- Medial temporal lobes are involved in memory
- STM and LTM are distinctly separate - HM was unable to move memories from STM to LTM (memory consolidation problem)
- Memory may exist but not be recalled - HM exhibited a skill he does not know he has learned. Explicit and implicit memory.
- Explicit - conscious memories, knowing-what
- Implicit - unconscious memories - knowing how (i.e. HM showed intact motor learning).
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Medial Temporal Lobe Amnesia
- Not everyone was this form of amnesia are unable to form new explicit long-term memories - as with the case with HM.
- Semantic memory (general information) may function normally.
- Episodic memory ( events that one has experienced) may not function normally. Able to learn facts, but not able to remember doing so (the episode that had been learned).
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The hippocampus and object-recognition memory
The hippocampus and consolidation
- HM has retrograde amnesia.
- Perhaps the hippocampus stores memories temporarily in order to consolidate.
Object recognition memory
- Early animal models of amnesia involved implict memory and assumed the hippocampus was key.
- 1970's - monkeys with bilateral medial temporal lobectomies show LTM deficits.
- Like HM, performance was normal when memory needed to be held for only a few seconds.
Object-recognition and Medial Temporal Lobectomy
- Bilateral removal of the rhinal cortex results in object-recognition deficits (if damaged).
- Bilateral removal of the hippocampus produces moderate effects on object recognition
- Bilateral removal of the amygdala has no effect on object-recognition.
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The hippocampus - theories of function
- Rhinal cortex plays an important role in object recognition.
- Hippocampus plays a key role in memory for spatial location.
Theories of Hippocampal Function
- Cognitive map theory - constructs and stores allocentric maps of the world.
- Configural association theory - involved in retaining the behavioural significance of combinations of stimuli.
- Involved in recognizing spatial arrangements of objects.
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Where are memories stored?
- Each memory is stored diffusely throughout the brain structures that were involved in its formation.
- Hippocampus - spatial location.
- Rhinal cortex - object recognition.
- Medidorsal nucleus - Korsakoff's
- Basal forebrain - Alzheimer's disease.
- Damage to a variety of structures results in memory deficits.
- Inferotemporal cortex - visual perception of objects.
- Amygdala - emotional learning - leads to lack of learned fear.
- Prefrontal cortex - temporal order of events and working memory.
- Cerebellum - sensorimotor tasks - conditioned eyeblink.
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