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week 11

by: Emma Notetaker

week 11 NSCI 4510

Emma Notetaker
GPA 3.975

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week 11
Biological Psychology
Dr. Colombo
Class Notes
25 ?




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This 6 page Class Notes was uploaded by Emma Notetaker on Friday April 1, 2016. The Class Notes belongs to NSCI 4510 at Tulane University taught by Dr. Colombo in Spring 2016. Since its upload, it has received 24 views. For similar materials see Biological Psychology in Neuroscience at Tulane University.


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Date Created: 04/01/16
Tuesday, March 29, 2016 Week 11 Memory Mechanisms-storage at cellular level • dual-trace theory of memory: • initial change (electrical) leads to eventual synaptic change • co-activity: network formed between multiple sensory systems if later, you activate (via recall) some part of the same network, ALL the areas become • reactivated (co-activity maintained) —> leads to recollection • model of long-term memory storage: multiple units in each area • subcortical regions have fast-changing connections to cortical regions (very plastic) • connections between cortical regions are slow-changing • if everything is plastic, model collapses - requires some connections to be slower stages • • encoding (consolidated over time) • memory resides in hippocampus • retrieval of memory before consolidation • retrieval cue reactivates network in hippocampus, which reactivates connections (still subcortical) retrieval of consolidated memory • • eventually, other cortical connections become stronger • now, there is no longer a need for the hippocampus - all connections in cortex • experiment: raised rats in different conditions • standard condition • social interaction, but boring environment impoverished condition: • • isolated, boring environment • enriched environments • social AND enriched environment • measured “branchiness” of apical and basal dendrites • no change in branching of apical dendrites in basal dendrites, in higher order branches (3rd order and above), enriched • environment showed MUCH more branching • experience changes actual brain structure • quick changes (synaptic) • involve synaptic transmitters (as a result of experience) • after training: change may be presynaptic (change in neurotransmitter release), postsynaptic (change in receptive zone) OR both • leads to increases PSP • involve interneuron modulation • increase neurotransmitter release via stimulation from another neuron • slow changes (structural) - long term • formation of new synapses rearrangement of synaptic input • • long-term potentiation: cellular model of long term memory • method of studying memory phenomena at cellular level • sections of hippocampus resemble two “C’s” intersecting (2 cell body layers) • cell layers: make up the “C” 1 Tuesday, March 29, 2016 • CA: made up of tightly-packed pyramidal cells • CA1 and CA3 dentate gyrus: made up of dentate granule cells • • trisynaptic circuit: • dentate gyrus • CA3 • CA1 • 3 pathways: perforant pathway: main input from entorhinal cortex • • synapses on dentate granule cells in dentate gyrus • mossy fibers • from dentate gyrus to CA3 • Schaffer collaterals • CA3 to CA1 information leaves after CA1 • • discovery: • artificial stimulation - recorded response from cells down the line in the hippocampus • recording response of CA1 from 2 different inputs (stimulated dendrites) • stimulate and record response • input one: gives a baseline (stimulated same place and record EPSP in CA1) give “zap” - tetanus (high frequency stimulus) • • come back later and give EXACTLY the same input (input 1) that caused the baseline responses • these same inputs caused DIFFERENT responses —> stronger response • —> potentiated response (cell responds differently to same input) • this potentiated response lasts forever: permanent change • input 2 did not show the same response • stimulus of input 2 remained at baseline after tetanizing input 1 • whatever changed after tetanus to input one MUST be specific to the area • change cannot be at the level of cell body • change occurs at a specific SYNAPSE (proven by the fact that input 2 did not show the same response) • if it was in the cell body, than input 2 would cause the same change • not a general change • synapse specificity - neural plasticity occurs at the synapse • LTP can also be reproduced via a “normal” amount of stimulation (instead of tetanizing) • mechanism of change: at synapse • normal synaptic transmission: glutamatergic example • release of nt into receptors • depolarization occurs • AMPA receptors: sodium channel • when glutamate binds, opens and sodium comes in • NMDA receptors: calcium channel • when glutamate binds, channel blocked by magnesium • under normal conditions, Mg block prevents ions from flowing • LTP induction: • AMPA receptors still activated • strong depolarization causes Mg block to LEAVE pore of NMDA • now calcium can enter (leads to activation of protein kinases) 2 Tuesday, March 29, 2016 • initiates MANY events - turns on many enzymes • this leads to short term changes: inserts AMPA receptors (postsynaptic change to increase cell receptivity) - • increases PSP • increase CREB (transcription factors) - makes new receptors, new ion channels, etc • CREB leads to retrograde signal generators • also leads to long term changes synapse enhanced after LTP • • CREB binds to genes with CRE sequence • genes activate changes in ER (transcription/translation of proteins) • proteins inserted in synapses (receptor subunits, ion channels, etc.) • Hebbian coincidence detector: if there is no co-activity (activity of BOTH pre and postsynaptic), no plasticity will occur NMDA is a coincidence • • requires pre and postsynaptic activity AT THE SAME TIME • conditioning dependent on overlap in time (must PAIR UCS and CS) • is LTP associative? • normally, sensory neuron has “strong” synapse to motor neuron (ex: shock, freeze) - automatic response input from a conditioned stimulus is a “weak” synapse • • requires a pairing with the strong stimulus to evoke a response (pre and postsynaptic activity must co-occur) • NMDA receptors must be activated by the strong synapse of the initial stimulus • postsynaptic cell depolarized enough to remove the Mg from NMDA • now calcium involved - synapse is strengthened (no longer need the UCS - conditioned stimulus now causes the cell to fire on its own) • associativity in hippocampus • hippocampal CA3 gets afferents (perforant path, mossy fibers, commissures) • stimulate commissural projections: baseline • tetanizing stimulus causes increase in PSP in commissures (coincident activity in commissural areas, none in mossy fiber areas) • no change in mossy fiber input (due to synapse specificity) • later, come back and stimulate mossy fibers (below threshold) • if this occurs at the same time as stimulating commissural fibers, will allow the mossy fibers to create PSP even though it didn’t reach threshold • experiment: • technique: optogenetics • can genetically engineer animal to express protein that responds to blue light • allows you to activate those cells by light exposure • better than other genetic changes (because usually animals raised with these genetic changes) • this allows to turn genes on and off whenever you want throughout their lifetime • changes receptor of rhodopsin • expression dependent on diet • when cells active, rhodopsin channel expressed • animal taught something AFTER activation of cells • almond smell means safety (no shock) • vinegar smell means shock (fear conditioning) 3 Tuesday, March 29, 2016 • after animal taught, blue light activates all these cells AGAIN (without the actual vinegar smell) because these cells were active when they learned to fear the vinegar smell, activation • via the light (which activates rhodopsin channel) causes the rats to FREEZE • fear memory turned on/activated • cellular representation of fear memory activated —> freezing • memory implantation - reactivating memory via different stimuli Attention • attention is very linked to time • selective process - focusing conscious awareness • exogenous processes: draw attention (ex: someone makes a loud noise) • bottom-up • endogenous: top-down • voluntary, conscious processing • initiated by subject • typically tested where the dependent variable is the reaction time attention is independent of the sensory world • • while fixed on a visual point, can fixate covert attention to different area • multi-tasking has limitations - very effortful, difficult • can (to some extent) attend to two things • sensory input —> attention —> motor output • visual input circuit signal hits retina, transmitted to LGN • • LGN —> V1 (processes features to a whole)—> v2 —> v4 —> IT —> PFC (assessment) —> premotor —> primary motor —> spinal cord —> movement • making decision about something (ex: choosing color of button) versus simple reaction time (ex: hit button when see light) • timing of decision recorded, then simple reaction time subtracted information not conclusive • • Posner tasks: endogenous shifts of attention (top-down process) • fixation point on computer screen • symbolic cue shown (arrow - says to look a certain direction) • have to covertly (while still fixating on dot) put attention in separate area of the field • delay occurs, then target appears dependent variable is reaction time • • valid trial: attention pointed to where the target will be • invalid trial: attention pointed away from where the target will be • neutral trial: arrow points both ways • results: valid trials reduced reaction times of locating target • exogenous: peripheral spatial cuing task attentional shift due to outside stimulus • • similar to above task, but now the cue occurs in a specific place • draws attention to the quadrant of the cur • invalid trial: cue in opposite quadrant of target • results: there is a difference in effect on reaction time based on interval between cue and target 4 Tuesday, March 29, 2016 • valid cues lower reaction time IF delay is less than 200 ms • however, if delay above 200ms, function reverses and valid trials actually increase reaction time • this phenomenon is called inhibition of return • thought to be because this cue is deemed un-useful by the conscious mind • has to do with how predictive something is - how linked it is • exogenous attentional system is rapid, but only useful for short period of time • endogenous take longer to occur, but more stable doesn’t decay is function is related to the given task • • visual search: filtering process - attention is focused • feature search: searching for single feature among other things of different features • ex: finding green object among red ones • seems to pop out • reaction time isn’t really affected by number of distractors (ex: if searching for something green, adding more red things won’t make it more difficult) • independent of number of distractors • conjunction search: searching for more than one feature • ex: finding red circle among red and green circle and squares • much more difficult - takes more time • solved binding problem: how does the brain figure out what constitutes object, and what is part of another object? • how do we know what things go together? • feature integration theory: brain looks for different features in parallel • overlays two cognitive maps (ex: red map, circle map) at the same time • multiple cognitive feature maps operating in parallel are what we learn to construct by experience as we grow up • over time, we come to learn how all these different components come to form objects • people who have grown up blind that are given sight really struggle with interpreting the world • too much visual stimulation - can’t figure out how to distinguish objects • EEG has great temporal resolution, okay spatial resolution • event-related potentials: measures brain activity (via EEG) in relation to stimulus • at each electrode, looking for coordinated activity • have to present stimuli over and over again (effect of particular trial very noisy - have to smooth the data by overlaying many trials) • eventually - ERP shows that stimulus causes meaningful activity • eearly signals: driven by early sensory processes (bottom-up) • P1: positive potential at 100ms (small) • N1: negative potential from baseline (150ms) • P2: positive potential at 200 ms • N2: follows P2 • later signals: associated with higher cognitive functions (top-down processes) • P3: LARGE positive potential • ERP changes in Posner task: endogenous visual attention test (cued) • for valid and invalid cues, P1 and N1 are potentiated - neural signal in the occipital lobe ENHANCED • only cognitive areas different • changing attention alters electrical activity • ERP changes in Posner task: exogenous visual attention 5 Tuesday, March 29, 2016 • short delay for valid cue: enhanced activity • short delay for invalid: not as much with long delay: more activity with invalid cue • • neural findings match with behavioral findings • attention and fMRI activation in visual cortex - where is brain active? • subject asked to covertly attend to one location (Att1) - increased activity in region as targets attended to them • when subjects asked to divide attention to 2 different areas in different visual fields (Att1 and Att2) - increased activity in both areas • if split more than two ways - maps start to diffuse • also, cannot be in the same visual field - must be able to dedicate hemisphere to one • some ways that attention can modify single cell activity • single cells tuned to respond to particular orientation (orientation-selective) • changes from attention: 1. increase rate of firing (enhanced or suppressed response) • • 2. sharpened tuning to specific stimuli (instead of responding more broadly, focus is sharpened • 3. tuning shifted to favor different stimulus • effects of selective attention on activity of single visual neurons • symbolic cuing (monkeys) attention directed to place where cue will arise (to correctly oriented bar) • • horizontal bar will drive cell, vertical bar will not • both bars in visual field • when attention directed, firing increased • when attention directed to ineffective stimulus: cell response changes • attention does alter single-units through enhancing or diminishing response of cell • attention can remodel receptive field • attending to particular stimulus • A: heightened sensitivity while attending to location (cell fires more while attention directed to stimulus) • B: same stimulus, but animal is attending to different position • reduces firing • C: LARGE shift in areas of neuronal reception • attention is not necessarily temporary response 6


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