Beth-brain Mech Of Memory Flashcards
Memory uses
Affects perception e.fb visual illusions. Attention like cocktail effect and what route to take. Personal I’d and culture . Learn from mistakes . Clive wearing- amnesia due to encephalitis, only got 20ms stm but procedural not effected
Patient HM
Surgeon did bilateral medial temp lobectomy to treat epilepsy. Studied by Milner. All anterior hippo, cortex and amygdala affected and some posterior. Anterograde amnesia (no memory since operation) and some retrograde (11 years before but childhood still there). Hippo for new learning and storing recent. WM and procedural fine
Regions involved in memory
Hippo: long, anterior at front, runs along medial temp lobe. Output is the fornix, projects to basal forebrain esp. Mamillary body (often damage in amnesia), gateway from fornix to thalamus which feeds back to cortex
Stroke doesnt cause amnesia as on the inside? So not due to blood flow
Other causes of amnesia - also damage the medial temp lobes
Anoxia (shortage of 02 reaching brain as fast metabolic rate) head injury in hippo, thalamus and frontal (damage to white matter and forbid). Herpes enters by olfactory nervesaffects hippo and anterior temp. Kosakoffs syndroms affects mammillary bodies, frontal and hippo due to lack of thiamin. aD but also has other issues like Lang
Impairments in amnesia
Deficits: verbal, visual learning. Not affected: STM, semantic, implicit, procedural and priming fine. stm is conscious-. Only impaired when info must be retrieved without rehearsal.
Patient EP
Amnesia from herpes simplex encephalitis. No episodic memory but semantic and stm fine unless no rehearsal. Can’t do word pair task but can copy figure. Priming fine
Implicit classical conditioning
Claparede 1911: handshake W pin, later p refused to shake hands but didn’t remember the doctor. Milner 68: asked to trace star in mirror, HM got better W practice but had no explicit memory. Graf 84: shown words in test then did word completion task- asked to fill in word seen before or any word. Amnesia normal at implicit
The memory systems- write out
Stm or ltm. Ltm split into decorative or non. Declarative split into episodic and semantic. Non has procedural condition and priming. Only episodic affected in amnesia
Representational spaces
Hippo has diff cortical reps for diff things e.g. place object and character. When go back, all other aspects as cued to reactivate representation (hippo binding). More active hippo, more likely to remember rep
Hippo structure
Looks like onion, tightly folded cell fields/distinctive. Input from dg, links between CA3 and CA1, then output from subiculum. Next to the temporal neocortex, the entrohinal cortex is gateway between hippo and neo. Perirhinal cortex and parahippocampal cortex for object id and spatial layout - project info to hippo. Olfactory goes into entrohinal then peri and para have links to learn about familiar objects
Anterior and posterior
Posterior has greater input from parahippo cortex , has spatial memory
Anterior has greater input from amygdala and perirhinal cortex for emotional memories, item familiarity
Synapses in memory
Individual neurons reflect structural changes at the synapse in ltm
Hebb 1949: memories are stored in connections between neurones called cell assemblies, ltm via hebbian learning in cells that fire together wire together
In brain, this happens bc of long term potentiation
Ltp background and study axample
Release of exc nt/glutamate means some Na channels open but if lots released, more channels open for longer so more Na in so causes ap- strengths comm at this synapse so post respond more strong next time. Bliss and lomo 73: single pulse to path triggers slight depol but if only do high freq pulses to one, saw change in volt when single pulse then given- single enough for ap
Ltp specific process
Between CA3(pre) and CA1 (post). Post has 2 receptor cells: AMPA and NMDA. Glutamate binds to ampa, nmda allows Na but also ca but blocked by mag so it can’t get in. When ap, glutamine binds to ampa. In high frequency, more glut so more depol in ampa, causes large depol which repels mg in nmda so Na and ca enters nmda. Large amounts of ca increases ampa receptors- over time see more glut in pre, more ampa, terminal divides to more receptors so little glut triggers ap (called synaptic consolidation- also enlargement and division, new dendrite spines
Features of ltp
Can be induced from one high freq event e.g. important memory. Causes chnages that last for weeks. Only active synapses are increased- remember spec events
Spatial memory in animals- Morris
Morris water maze: rat in murky water, has to find hidden platform but remember location so swims there faster next time using room landmarks. Hippo lesions show posterior used for spatial but not ltp. Bathed hippo in nmda antagonist to block glut, shows nmda used for learning new info and ltp but don’t know where ltp occurs spec.
Transgenic mice
Tonegawa 96: gene splicing for mice to lack nmda in ca1 (knockout), showed impaired spatial learning but classical condition the same (amnesia). Tsien 96: knockout mic swim randomly so ltp in ca1 for spatial. Spatial and not procedural as release rat in diff positions so diff. Movements
Place cells
Neurones in ca1 that only respond to spec places/place fields-okeefe and dostrovsky. Theory that hippo provides internal map that codes for spatial relations between objects and environment
Spatial memory in humans
Maguire: taxi had bigger posterior, linked to time. Ekstrom 2003: for drug resistance ep, take out small part of hippo but have microelectrode to see where surgery coming from. During this, did vr navigation and found place cells in hippo, parahip cortex, amygdala and frontal
Theory 2: relational memory
Eichenbaum and Cohen: rats w hippo lesions can remember ind links but not relations. Used transitive inference task- rats dig through beaker to find food, did diff pairs where one rewarded. Should search one more than the other but W lesion, search both equally
Theory 3: recollection vs familiarity
Hippo used in mental time travel as need relations between items and contexts. Familiarity is form of declarative memory as conscious. Related to priming in the perirhinal cortex. Ps asked to tell them if remembering or just feeling familiar e.g. word from a list. Remember show hippo boots but not in familiar
