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Unformatted text preview: Learning & Memory
Anand Acharya Ernie Scelia Introduction: Learning and Memory Handinhand Gives us ability to acquire and store information necessary to life. 5% of people over 65 and 20% of people over 80 have suffer from Alzheimer's disease. Memory Memory takes place at the over 10 trillion synaptic connections. Due to small size and overwhelming abundance, identification of the sites where memory is stored is nearly impossible. Enter, Karl Lashley... Karl Lashley One of the first scientists to examine location of memory. Attempted to research anatomical site of the memory trace or what he called the engram. Influenced by Ivan Pavlovdiscovered form of learning called classical conditioning. Dog presented w/ food, salivation=Unconditional. Dog presented w/ tone related to food=Conditional. Cerebral cortex stored memory. 510% removed, no effect but large portions removed, great effects. Donald Hebb Hypothesised that shortterm memory of each experience is stored by neural activity reverberating in closedloop CNS circuits If reverberating for a long time, it produces structural changes in synapses and facilitates subsequent transmission over the same pathway. Hebbian Synapse is a synapse strengthened by learning. The brain Cerebral cortex is the primary site for sensations, perception, voluntary movement, language and memory storage. Neocortex (top six layers found only in mammals) Cognition and memory Hippocampuscrucial role in storage and consolidation of long term memories. When damaged=amnesia. Theories of medial temporal lobe function William Scoville and HM Removed patient HM's medial temporal lobes to eliminate seizures (including amygdala and hippocampus) Found profound effect on HM's memory: resulted in anterograde amnesia HM maintained ability to maintain verbal shortterm information but not nonverbal ST information Cohen and Squire Hippocampus is responsible for formulation of memory but not of actual storage HM has impairment of declarative but not procedural memory Similar idea is explicit v. implicit memory Tower of Hanoi test v. Finger maze Korsakoff's syndrome Sergi Korsakoff: diencephalic amnesia Caused by thiamine deficit/poor diet/reliance on alcohol Associated with damage to diencephalon region Symptoms/results Wernicke's encephalopathy Severe deficit in learning new information Retrograde amnesia Posterior and dorsomedial thalamus always damaged Recent support for theory Papez and Yakovlev circuits intro. 2 Separate regions where damage from amnesia results Hippocampus Amygdala Both are anatomically connected Both are crucial to memory Papez circuit Connects limbic system to cerebral cortex Pathway: Damage to Fornix causes anterograde amnesia 1.cyngulate gyrus 2.hippocampus 3.mammillary bodies (via fornix) 4.anterior thalamus (via millothalamic tract) 5.cyngulate gyrus Fornical relay of hippocampal information to diencephalon region likely to be crucial for long term memory. Studies show level of damage correlates to level of memory impairment Yakovlev circuit Connects to dorsomedial thalamus Focal point at amygdala Pathway: 1.amygdala 2.dorsomedial thalamus 3.orbitofrontal cortex 4.amygdala Animal studies have shown damage to amygdala causes memory impairment Evidence from animal studies Hippocampus is involved in memory, therefore removal should cause impairment. Memory impairment has been shown in areas of working memory and cognitive mapping to hippocampallesioned rats. However, studies did not always support impairment in hippocampallesioned rats. Working memory Evolutionary importance of WM Olton Radial arm maze Hippocampallesioned rats did not perform efficiently 2 Possible explanations 1.working memory deficit 2.cognitive mapping deficit Made second maze (more complex) to test possibilities Hippocampallesioned rats showed "reference memory" but performed at chance otherwise Showed cognitive mapping capacity, but not WM. Cognitive mapping John O'Keefe Morris Recorded electrical activity of individual hippocampus cells in rats Discovered "Place cells" Spatial memory task Water maze with hidden escape platform Contradicts Olton's finding of "reference memory" Hippocampallegioned rats were unable to perform efficiently even after 40 days of training. Currently, reason is unclear why these tests yield different results Memory task involving primates Delayed nonmatched sample procedure Hippocampallesion caused little impairment (75% accuracy v. 90% accuracy, control) Dorsomedial thalamic lesion Seems to contradict human response Greater impairment (62% accuracy v. 90% accuracy, control after 10 min delay) Additional studies Mishkin Made lesions to hippocampus or amygdala in macaque monkeys Made lesions to hippocampus and amygdala Neither lesion caused much impairment (90% accuracy after 2 min delay) Greater effect (60% accuracy after 2 min) Suggests both regions are important for memory processing. Each is part of a different memory circuit, and so possibly both must be damaged for serious amnesia to result. Additional studies cont. Mishkin's studies also encouraged additional temporal lobe study Including: Each of these areas also created impairments in delayed nonmatching task This medialtemporal lobe contains several regions collectively important for memory. Cortical tissue surrounding hippocampus Perirhinal cortex Parahippocampal gyrus (including entorhinal cortex ...
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- Spring '07