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Lecture 6

PSYCH 309 - Lecture 6 (Memory Representation) - Sept 23.docx

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University of British Columbia
PSYC 309
Todd Handy

September 24, 2013 – Lecture 6 Readings: H.M., an Unforgettable Amnesiac, Dies at 82 • Henry Gustav Molaison – died of respiratory failure in nursing home • 1953 – underwent experimental brain operation in Hartford to correct seizure disorder o 9 years old, banged his head after being hit by bike rider o Blacking out frequently, devastating convulsions, no longer repair motors to earn a living • Developed profound amnesia – lost the ability to form new memories o Did not damage his intellect or radically change his personality • Participant in studies for 55 years, helped scientists understand biology of learning, memory, physical dexterity, fragile nature of human identity • Dr. Scoville decided to surgically remove 2 finger-shaped slivers of tissue o Seizures lessened; procedure cut into hippocampus, left patient radically changed • Dr Milner, gave him variety of memory tests, alter understanding of learning and memory o Trace outline of star – new experience every time, no memory of doing it before o With practice, he became proficient • 2 systems in the brain for creating new memories o Declarative memory – (facts, events) records names, faces and new experiences, stores them until consciously retrieved, explicit memory  Episodic memory + Semantic memory  Function of medial temporal areas, hippocampus o Motor learning – subconscious depends on other brain systems (skills, how to do things)  Pick up guitar and remember how to strum it • H.M.’s short-term memory fine – hold thoughts for 20 seconds, without hippocampus • Gist memories – had the memories, but couldn’t place time, couldn’t narrate it Future Decision-Making Without Episodic Mental Time Travel – Kwan, Donna • Deficits in episodic memory – inability to imagine future experiences (ie. mental time travel) • K.C. – episodic amnesia, bilateral hippocamppal damage in motor cycle accident, inability to imagine future experiences, unable to recall past personal event o MRI scans – extensive volume loss in medial temporal lobe structures (hippocampal formation, surrounding parahippocampal gyrus bilaterally) o Systematically discounts value of future rewards o Neither able to imagine personal uses for rewards nor provide rationale for selecting larger future rewards over smaller  Dissociation between imagining and making decisions involving the future • Hippocampal damage + episodic memory impairment = impaired ability to imagine the future • Imagining future episodes requires one to orient oneself to a future time and construct narrative of an event at that time • Hippocampal amnesia – deficit in event construction; task did not require temporal orientation o Temporal orientation and event construction might be independent processes • Boyer – hypothesized that capacity to imagine future rewards has evolutionary function of counteracting tendency to discount future rewards o If so, K.C. would devalue future, larger reward and have selective bias toward immediate reward (unlike controls) given he is unable to imagine the future • Luhmann – argued that people imagine the wait period itself and the unpleasantness of waiting for delayed reward biases subjects toward immediate rewards o K.C. (unlike controls) should not exhibit a bias toward choosing smaller, immediate reward; choose larger reward • One would expect KC to show a nontemporal strategy in his decision-making o Choose immediate or later reward according to 2 hypotheses • Pattern of preserved semantic and impaired episodic memory abilities ahs remained stable since time of accident • KC within range of controls o Showed magnitude effect (shallower discounting of larger delayed amount) • KC – extensive hippocampal damange, resulting episodic amnesia o Still values future rewards, despite being unable to construct details of past/future o Discount delayed rewards relatively steeply; may reflect damage to his hippocampus o Dissociation between ability to value future rewards & ability to imagine experiencing future rewards
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