×
Log in to StudySoup
Get Full Access to Tulane - NSCI 4510 - Class Notes - Week 17
Join StudySoup for FREE
Get Full Access to Tulane - NSCI 4510 - Class Notes - Week 17

Already have an account? Login here
×
Reset your password

TULANE / Neuroscience / NEUR 4510 / what is the meaning of hippocampus?

what is the meaning of hippocampus?

what is the meaning of hippocampus?

Description

School: Tulane University
Department: Neuroscience
Course: Biological Psychology
Professor: Colombo
Term: Spring 2016
Tags:
Cost: 25
Name: Study Guide Biopsych Exam 3
Description: Comprehensive study guide including book and lecture notes.
Uploaded: 04/21/2016
25 Pages 4 Views 15 Unlocks
Reviews


Thursday, April 21, 2016


what is the meaning of hippocampus?



Exam 3 Study Guide

Memory Systems  

• opposing theories

• memory is property of cells - everywhere in the brain

• memory stored in specific locations (localized)

• working memory is NOT short term memory

• get rid of it once you complete task - time varies

• ex: have to remember where you parked

• HM: bike accident caused debilitating seizures

• localized in hippocampus (excited primarily by glutamate)

• hippocampus especially sensitive to excitation

• surgeons removed medial temporal lobe (bilaterally)

• removed hippocampus and amygdala

• HM awake for this

• no change in IQ, intellect intact

• lost ability to form ANY new memories (global anterograde amnesia)

• lost EPISODIC memory (declarative/explicit)

• if asked who the president was, would say it was whoever was president before his  accident


what is spatial memory?



• lost ability to be trace conditioned

• normal short term memory, could carry out conversation

• this area deemed the first memory system (in 1957) due to his case

• subjected to many tasks testing his intact skills

• mirror tracing: motor skill learning

• got better and better as he learned - remembered from day to day

• RETAINED ability to learn motor skills

• suggests that hippocampus is not the only area of the brain where memory resides • word-stem completion task: priming

• exposure to information, then fill in the end of words

• amnesics do just as well, if not better, than controls with word completion • medial temporal lobe removal: can still store information, just not in explicit fashion • with priming, there is a decrease in activity in brain areas - brain operates more  efficiently  We also discuss several other topics like What are the tragedy of the Commons?

• classical conditioning: paired tone with air puff into the eye


what is Eichenbaum?



• people start to associate tone with blinking

• delay conditioning: delay between onset of tone and onset of air puff

• tone stays on throughout duration, still on when air puff comes

• CAN be learned with medial temporal lobe amnesia

• trace conditioning: tone still before, but leaves before air puff

• medial temporal lobe amnesics CANNOT be trace conditioned

• intact skills:

• learning motor skills

• priming

• delay conditioning (simple classical conditioning)

• medial temporal lobe amnesia (mostly hippocampus)

• impaired:

1

Thursday, April 21, 2016

• declarative memory

• episodic: events of your life

• semantic: facts

• dissociated from time and place - don’t always know where/when you learned it • probably stems from episodic memory If you want to learn more check out What is Voltage-gated Na+ channels?

• intact:

• nondeclarative (procedural memory)

• skill learning

• priming

• conditioning (simple - delayed)

• time courses of memory - 2 kinds of memory storage

• extent of the two very variable

• short tem

• rapid

• no structural change - in terms of neural activity

• labile - unstable

• strength decreases with time

• occurs first

• long term

• slow

• building new synapses - structural changes

• strength increases with time

• stable We also discuss several other topics like What is international relations?

• occurs after short term

• recall test:

• controls recall more items from beginning (primacy effect) and end (recency effect) of the  list - forget most from the middle We also discuss several other topics like What is a consequent?

• end of the list still in short term memory

• things from beginning of the list have started to be consolidated to long term memory • amnesics remember things from the end, NOT from the beginning

• because their long term memory is the issue

• if no delay, ONLY recency effect

• with intermediate delays, get primacy and recency effect

• with VERY long delay, no recency effect (only primacy)

• most recent items have not been in long term, while the rest have

• too long to still use the short term memory

• animal models of amnesia: hippocampal damage in rats

• normal (or better than normal) acquisition of standard (Skinner) operant conditioning tests • conflicting findings with spatial and sensory discrimination tasks

• y maze: sensory discrimination

• simultaneous visual discrimination (see both black and white)

• one arm is black, one is white

• one color will be rewarded - rat learns which one it wants

• rewarded arm switches positions after delays - seeing if they will choose the correct  color for reward

• INTACT with hippocampal damage

• other y-maze task: SPATIAL discrimination task

• concurrent visual discrimination (see EITHER white or black, never both together) • rat will see two black or two white inserts Don't forget about the age old question of what is paleomagnetism?
We also discuss several other topics like What is the substructure of the neuron in human physiology?

2

Thursday, April 21, 2016

• if white, have to turn left

• if black, have to turn right

• IMPAIRED with hippocampal damage

• found that hippocampus important for SPATIAL memory

• water maze task: spatial navigation (Morris)

• hidden platform in opaque water - rat has to find it

• started from different locations, but platform remains in the same location • place navigation: have to find the platform (that remains in the same place) • normal animals learn rapidly over the first few trials - takes shorter time to get to it  with repeated studies

• lesioned cortex: no effect

• lesioned hippocampus: NEVER do as well as controls

• cue navigation: put something else to cue where the platform is (platform may move) • rats with lesions of cortex and hippocampus so JUST as well as controls • showing that they are able to swim to cue shows that they’re still motivated, motor  skilled and able to process sensory information

• probe trials: move platform

• cortical lesion and controls spend more time looking where the platform used to be • lesioned hippocampus spend equal time in each quadrant - do not remember that  the platform was in a specific location

• conclusions:

• hippocampus has nothing to do with vision, motivation, motor skills

• hippocampus is related to spatial navigation

• lesions to hippocampus can still have decrease in latency, but don’t have spatial  bias

• Olton: hippocampus NOT necessary for spatial memory, but working memory • critique of Morris - not all spatial memory impaired (reference memory intact, working  memory impaired)

• radial arm mazes: animal placed in center, food placed in separate arms • A. once baited arms: optimal performance means going in each arm once • tests working memory (have to remember which arms you’ve visited)

• only want to remember this for a day - irrelevant for next trial (have to start over) • hippocampal lesions caused IMPAIRMENTS (spatial memory task)

• B. reference memory task

• some arms baited, some NEVER baited

• now animal has to learn to go to the baited arms and not go to the ones without  bait  

• hippocampal lesions could still remember reference memory (knew which ones  never had food), but struggled with working memory (knowing which ones they’d  been to already)

• C. working memory task - each arm a different texture  

• NON spatial working memory task

• move order of textures every day

• go in each texture only once per day

• hippocampal lesions IMPAIRED

• shows that not spatial memory that is impaired, but working memory • however, reference memory was impaired in the Morris task…inconclusive • some evidence supports each hypothesis

• inferential memory expression - not spatial

3

Thursday, April 21, 2016

• Eichenbaum

• animals learn paired associates (hippocampal lesions are still intact - can still learn simple  associations)

• odors paired with other odors

• if given A, food reward paired with B (not with Y)

• if given X, food reward paired with Y (not with B)

• then go to another set

• given B go to C

• given Y go to Z

• test for transitivity:

• given A: see if they go to C (because A—>B—>C)

• given X: see if they go to Z (because x—>y—>z)

• SEVERELY impaired with hippocampal lesion (controls are fine) - cannot learn the rule • summary:

• 1. various kinds of learning, spatial, non spatial, simple and complex can be accomplished  WITHOUT the hippocampus in animals and human amnesics

• 2. hippocampus REQUIRED to link representations of overlapping experiences into a  relational representation

• necessary for flexible and inferential expression of indirect associations among items  within larger organization of linked memories

Memory Systems (cont.)

• 3 main memory systems (can be dissociated, but not completely separate) • 1. hippocampus

• 2. amygdala

• 3. dorsal striatum

• early evidence showed that these areas can be dissociated, but later evidence shows that  there is an interaction

• stress and time can cause a shift between memory systems

• sometimes they compete, sometimes they cooperate

• double dissociation experiments: hippocampal and striatal memory systems SEPARATE • win-shift strategy: radio arm maze

• reward in arm, “win” by getting food reward  

• once the rat gets the food in one, has to go to the others

• hippocampus-dependent: working memory

• lesions in hippocampus impair this task

• lesions in striatum have no effect on performance

• requires spatial, flexible and relational memory

• win-stay task: radial arm maze

• there are cues in the maze - ex: light indicates presence of food

• if the light is still in the same arm, can go back to that one to find more food • procedural/rule-based memory

• based on striatum (lesions here impair this task)

• hippocampal lesions have no effect here

• triple dissociation experiment:

• investigates roles of:

• hippocampus: implicated flexible/relational memory

4

Thursday, April 21, 2016

• win-shift: each arm baited with food reward (if rat goes back into that arm, will be  empty)

• optimal performance: goes into each arm once (8 choices)

• repeat this for several days

• S-S: stimulus-stimulus (associations among stimuli - map tells you relationally  where reward is)

• fornix lesion: cuts connection to hippocampus

• shows SOME improvement, but never get as good as the sham/controls • sham lesion: no actual lesion (mimic the dramatic effects of the surgery) • show lots of improvement, learn quickly

• control animal: show lots of improvement, learn quickly

• lesion to the lateral amygdala: do BETTER than controls (or no effect - unclear) • does not impair performance

• lesion to dorsal striatum:  

• striatum: implicated in procedural/rule-based memory

• win-stay: 4 lit arms, 4 unlit arms

• after animal goes into lit arm once, light stays on  

• after going to the same lit arm twice, light goes off (to mimic 8 choices from win shift)

• S-R: stimulus response

• simple rule: go to the lit arm

• dorsal striatum lesion: impairs performance

• sham lesion: no actual lesion (mimic the dramatic effects of the surgery) • fornix lesion: no difference  

• lateral amygdala lesion:  

• amygdala: implicated in EMOTIONAL memory

• conditioned place preference

• animal placed in one arm with a pile of food (animal conditioned into a preference  for this location)

• subsequent trial: put animal in an empty arm

• later test: put animal in the middle to see if it goes to the correct arm

• lateral amygdala lesion: impairs performance

• fornix lesion: no effect

• dorsal striatum lesion: no effect

• sham lesion: no actual lesion (mimic the dramatic effects of the surgery) • no effect

• control: no effect

• response learning takes longer than place learning

• plus maze: walls in shape of plus, put food somewhere

• place task: animal rewarded for returning to a place in space (independent of where you  start)

• food remains in the same place

• dependent on the hippocampus (lesions impair this)

• response task: animal rewarded for turning a certain way

• ex: food always to the right of wherever they start

• dependent on striatum (rule-based)

• place + response task (aka dual-response task)

• animal can use either hippocampus OR striatum to solve the task (as a researcher,  you don’t know which one the animals is using)

5

Thursday, April 21, 2016

• to test which one has been learned: probe trial

• flip the maze

• those who have been using response strategy will continue to turn the same way • those who have been using place strategy will go to the same place

• Chang and Gold (2003)

• trained animals on pace or response task

• administered lidocaine (local anesthetic - blocks voltage-gated sodium channels)  DIRECTLY to brain region

• acts as a temporary lesion - blocks neurons in that area from firing (temporary  inactivation)

• artificial CSF: inane substance

• place task: lidocaine into hippocampus impaired learning

• expected

• response task: lidocaine to hippocampus FACILITATES learning

• unexpected (response task thought to be only dependent on striatum)

• inactivation of hippocampus facilitates response learning

• theory: hippocampus and striatum compete with each other for control of behavioral  output

• hippocampus leaves, can focus all attention on striatal task

• —> interactive memory systems (NOT independent)

• micro dialysis: in vivo method of studying neurotransmitter release

• chronically implant dialysis probe

• hooked up to machine that analyzes concentration of different metabolites • depending on membrane, certain bodies cross membrane

• quantifies small amounts  

• can hook animal up, engage them in a task and see which neurotransmitters are coming  into play

• McIntyre experiment: using micro dialysis

• conditioned cue preference task

• measured ACh release in hippocampus

• percent time in correct arm STRONGLY decreased with increasing baseline levels of  ACh in hippocampus

• worst memory: most ACh release in hippocampus  

• taken as evidence of competition between amygdala and hippocampus • active hippocampus: poor amygdala results

• deactivated hippocampus: GOOD amygdala results

• later measured ACh release in amygdala

• used hippocampus-dependent task

• more ACh in amygdala correlated with BETTER learning on hippocampus-dependent  task

• evidence that amygdala activity facilitates other areas

• hippocampus competes with both striatum and amygdala - suppression allows for better  performance in tasks that require other areas

• amygdala can cooperate with hippocampus

• interactions across time:

• animals trained on dual solution task (ambiguous) - 100 trials

• early on: after first 20 trials - almost all animals used spatial strategy

• using hippocampus

• over time, more and more animals use response strategy

6

Thursday, April 21, 2016

• using dorsal striatum

• by the end: almost all the animals used the response strategy

• hippocampus used initially - good with association and explicit awareness • conscious awareness has a limited field, so needs to be passed off to striatum  • signifies habit formation - procedural memory

• once it becomes a motor habit, skills begin to become dependent on the striatum • habit drives most of behavior

• “corticosteroids operate as a switch between memory systems” - Schwabe • hole-board task: animal placed in the center

• most holes are dead ends, one hole is an escape route

• in training: they get a cue AND a place (on the same hole)

• see which one they use (place or stimulus-response strategy)

• stressors and controls:

• untreated: ALL animals use spatial strategy (using hippocampus)

• vehicle injection:  

• corticosterone:

• restraint stress:

• aMR (cortisol receptor antagonist)

• animals in stressed conditions: some use response strategy

• findings: stress SHIFTS strategy away from hippocampus (explicit) to more procedural  (unconscious) memory

• spatial learners took longer than the ones who shifted

• shifting to procedural strategy improves latency to escape (helps to escape faster) • under stressful conditions, don’t want to sit around thinking about what to do  (evolutionarily)

• cortical association areas - all 3 memory systems associated with cortical areas  • olfactory

• prefrontal

• cingulate

• parietal

• temporal

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

7

Thursday, April 21, 2016

• 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”

• CA: made up of tightly-packed pyramidal cells

• CA1 and CA3

• dentate gyrus: made up of dentate granule cells

• tri-synaptic 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)

8

Thursday, April 21, 2016

• 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)

• 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?

9

Thursday, April 21, 2016

• 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)

• 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

10

Thursday, April 21, 2016

• 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  

• 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  

11

Thursday, April 21, 2016

• 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

• early 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

• 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

12

Thursday, April 21, 2016

• 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

Attention, Consciousness and PFC

• cortical regions implicated in top-down control of attention

• intraparietal sulcus (IPS): involved in top-down/volitional control

• dorsal frontoparietal system: cognitive control

• from frontal and parietal regions

• part of the dorsal stream (of visual information)

• frontal eye field: “where”

• attentional mechanisms, shifting gaze

• frontoparietal attentional control network:

• attentional control network

• dorsolateral frontal

• superior temporal

• posterior cingulate

• medial frontal

• target processing

• pre and postcentral gyrus

• cingulate cortex

• visual cortex

• supplementary motor

• ventrolateral frontal

• regions in endogenous attention

• intraparietal region

• frontal eye fields

• regions in exogenous attention

• ventral frontal cortex

• temporoparietal junction

• novel stimulus will go to ventral frontal cortex (after going to visual areas) • brain damage in hemispatial neglect

• hemispatial neglect: ignore half of visual space in absence of visual impairment • attentional/information processing deficit

13

Thursday, April 21, 2016

• damage to parietal and frontal regions (map on well to areas in the model for cortical  attention control network above)

• unconscious brain: examine

• coma: frontal and parietal inactive

• persistent vegetative state: prefrontal and parietal inactive

• sleep: frontal and parietal inactive

• general anesthesia: frontal and parietal inactive

• overall: regions of brain implicated in consciousness are prefrontal and parietal • consciousness involved in same cortical regions as attention

• communication in unconscious patients (coma, unresponsive)

• researchers able to make coma patients think of different things

• ex: motor act vs spatial act - asked to think about playing tennis vs. navigating • patient: when thinking about motor act, one area lights up

• when thinking about spatial act, a different area lights up

• different areas light up when they want to answer “yes” or “no”

• can determine their answer even though they are deemed unresponsive  • lots of brain damage, which grows as they stay vegetative

• experiment: act first, think later

• looks at volitional behavior

• series of letter that appear on the screen, letter changes every second

• instructed to press button whenever they want, using left or right hand

• notice letters as they go by, tell researcher when you made decision to press button • subject reports letter that the decided, BUT the decision making regions activated before • activity in decision making regions up to 10 second before reported decision • activity in motor cortex also up to 5 seconds before the person reports deciding to press  button

• person is unaware that they made decision until just before they actually make the motor  action

• brain acts and THEN conscious awareness interprets action

• prefrontal cortex: unique in humans

• different percentages of brain in other mammals dedicated - human proportion is greater  than other animals (29% of total brain)

• dogs are 7%, compared to cats which is 3.5% (dogs are smarter!!!)

• definition: area that receives projections from mediodorsal regions in thalamus • main divisions:

• dorsolateral PFC: sensory input/processing

• connections to motor areas - controls motor output and behavior

• ventrolateral PFC: sensory input/processing

• orbital PFC: linked to limbic system and basal ganglia

• affect, reward systems

• risk behavior

• expectancy outcome matches and mismatches

• assessing frontal function

• delayed match to sample task: symbolic (non-spatial)

• see sample (green light)

• delay

• see both sample and novel light (green and red) - have to pick the now you saw  previously

• look at effective cooling of bilateral portions (temporary impairment of region) 14

Thursday, April 21, 2016

• with little delay, very little separation

• at short delays, PFC not very involved  

• as delay increases, prefrontal cooling drops off greatly

• parietal cooling and normal temperature barely drops off at all

• results: parietal doesn’t contribute to these tasks, but PFC necessary (especially for  longer delays)

• PFC more important than parietal

• PFC not involved in attentional behavior, but more in memory

• delayed response task: spatial

• see cue

• delay

• see cue in same location it was in previously, have to pick right spot

• look at effective cooling of bilateral portions

• with little delay, very little separation

• as delay increases, prefrontal cooling drops off greatly

• parietal cooling and normal temperature barely drops off at all

• results: parietal doesn’t contribute to these tasks, but PFC necessary (especially for  longer delays)

• PFC more important than parietal

• PFC not involved in attentional behavior, but more in memory - higher order  cognition

• damage to PFC: little trouble in executing learned response to specific stimuli • PFC not involved in sensory discrimination

• if two different discriminatory stimuli not presented simultaneously

• conditional response: “go, no-go task”

• see green light and red light - press button with only green light to be rewarded (have to  NOT press when they see red)

• lesions to PFC: rats press light when they see red AND green - can’t learn to inhibit  response

• —> PFC implicated in inhibitory/impulse control

• Phineas Gage: tamping rod went through his eye, bilateral damage to PFC • mainly damaged his orbitofrontal and medial prefrontal cortex (didn’t hit his dorsolateral) • never lost consciousness

• studied by Harlow: “Gage was no longer Gage. Now exhibited inordinate profanity,  vacillation, capriciousness, poor planning, and uncontrolled impulsivity.”

• prefrontal syndrome: lose impulse control, can’t inhibit  

• tests for PFC dysfunction

• children very bad at these tasks as well, due to the fact that their PFC is underdeveloped • Stroop task: color of word is different than what the word says

• instructed to just say the color of the word

• people with PFC damage cannot do it - just say the word instead of the color • cannot inhibit the tendency to read vs look at the color

• Wisconsin card sort: different categories (shape, color, number)

• at first, don’t give instructions - just tell subjects right or wrong (experimenter has  specific category in mind)

• subject has to go until they find the right category

• after 10 rounds, experimenter randomly shifts the category

• normal people are responsive to shift

• PFC damage: show perseveration —> WILL NOT change category

15

Thursday, April 21, 2016

• unable to shift to a new pattern, will not try different strategies even though the current  one is not working anymore

• tower of London task:  

• 3 columns, get instructions (move one at a time, only move to adjacent pegs, etc) • have to move from start to goal

• PFC damaged individuals have lots of trouble with this

• planning and strategic behavior impaired

• cannot think ahead - goal-oriented behavior

• model of supervisory attentional mechanisms and executive functions (goals and means for  obtaining them)

• brain normally: sensory input goes in, processed, leads to behavior

• simple nervous systems: well established routines (sensory has few places to go before  motor)

• as brain becomes more complex, more stops between sensory and motor areas • shifting and changing connections in PFC

• executive functions acquire information about goals and means to select and coordinate  among innate and well-established routines. a

• active processing lines are indicated by red in the picture

• system measures outcomes (based on whether they meet goals) will change the pathways • well-learned habit system between sensory and motor

• executive functions suppress habits and allow for alternate connections and functions  between sensory and motor output

• children in music-based mentoring have increased rates of myelination in PFC • predicted acceleration in these children compared to controls

• frontal lobe is one of the first areas to degrade in aging: old people also struggle with the  above tests

• PFC is bridging temporal gaps in perception-action cycle

• immediacy between sensory input and motor output, but sometimes temporal gaps that  require bridging (impulse control)

• allows processing outside of “here and now” boundaries

Recent Research  

• dorsoparietal and frontal regions involved in endogenous attention

• right hemisphere (temporoparietal and ventral frontal) involved in exogenous attention • frontoparietal region: default mode areas

• “The Self-Pleasantness Judgement Modulates the Encoding Performance and the Default  Mode Network Activity”

• pleasantness judgement is a way to focus attention internally

• increase default mode network (DMN) activity

• seeing stimulus and rating it as pleasant or unpleasant causes you to come up with  internal representation - manipulates activation of default mode network

• pleasantly judged stimuli require internal drive (rely more on subjective judgement) • unpleasant judged externally (ex: threats - not adaptive to stop and think about it) • hypothesis: increase in default mode network activity increase memory recognition for  pleasant stimuli (internal), and decrease memory recognition for unpleasant things  (depends externally)

• behavioral intervention: present stimuli, measure brain activity as a result 16

Thursday, April 21, 2016

• independent variable: behavior (stimulus)

• dependent variable: brain activity

• procedure:

• used fMRI to evaluate effect of self-relevance in cerebral activity

• 21 participants (French, 10 male, 10 female)

• received sets of stimuli: words, faces or images  

• 6 batches of 30 (180 total)

• rated stimuli as pleasant or unpleasant (under fMRI)

• raise index finger for pleasant, middle finger for unpleasant

• told to go quickly - instantaneous impression

• 1 hour later, surprise memory recognition test (incidental encoding - not told they they  needed to memorize the items)

• not under fMRI

• DMN:

• precuneus

• cingulate

• mPFC

• lateral parietal

• results: memory recognition better for pleasant items

• behavioral results: in terms of encoding

• more successful encoding than unsuccessful

• interaction between pleasantness ratings and successful encoding

• faster reaction times with pleasant stimuli

• overall:

• more brain activity when rating as unpleasant

• significant interactions with temporal lobes

• look at 18.17-18.19 in book

• frontoparietal is endogenous, temporal is exogenous

• if internally focused, fail more with unpleasant recognition, succeed more in items  that were deemed pleasant

• posterior default mode network modulation by pleasantness judgment  • region of interest study:

• mPFC: significant increase in bilateral activity in pleasant vs. unpleasant • suggests mPFC involvement in self-referential processing (pleasant)

• lateral parietal lobe: significant increase in right hemisphere activity with pleasant  vs. unpleasant

• these two support hypothesis

• unpleasantness involved in activation in posterior areas

• successful encoding areas

• inferior frontal

• lateral temporal

• unsuccessful encoding:  

• posterior cingulate

• precuneus  

• increase in medial frontal and parietal DMN regions

• interaction between encoding performance and pleasantness

• unsuccessful encoding:

• precuneus: increase in activity with pleasant stimuli (inconsistent with  

hypothesis)

17

Thursday, April 21, 2016

• posterior cingulate: no difference between unpleasant and pleasant

• inferior frontal gyrus: increased in pleasant

• successful encoding:  

• precuneus: increase in activity with unpleasant stimuli

• posterior cingulate: pleasant is GREATLY increased (consistent with  

hypothesis)

• inferior frontal gyrus: increased activity in unpleasant judgments  

• “complex cooperation between DMN and task-successful regions” - parts of study fairly  inconclusive

Language

• auditory components, visual components (reading)

• association cortices don’t receive primary subcortical input

• comprehension and production of language can be dissociated

• speech

• phonemes: sounds of speech

• morphemes: multiple phonemes - syllables

• words

• semantics: meaning of words

• syntax: meaningful strings of words

• graphemes: multiple phonemes in writing (visual representation of morpheme) • some families have disproportionately high rates of language disorders • disorders of speech acquisition

• about half of each generation is affected

• linked to fox gene (transcription factor) - causes identifiable differences in brain structure • caudate nucleus

• inferior frontal gyrus

• inferior cerebellum

• William’s syndrome: separates language from intelligence

• fluid output of language, but significant IQ and spatial processing deficits • electrical stimulation various regions: find regions that interfere with language production OR  language comprehension

• regions cluster around inferior frontal and superior temporal areas

• usually left hemisphere (lateralized)

• aphasia: language deficit resulting from some kind of damage

• global aphasia: total loss of ability to understand language and speak

• Broca’s area: left inferior temporal lobe

• damage: deficit in speech production, but comprehension intact (non-fluent aphasia) • production and output of language (across different modalities)

• speech and/or writing (motor problems associated with communication) • Wernicke’s area: left superior temporal gyrus

• damage causes issues with comprehension of speech

• can produce speech though it is not particularly meaningful

• fluent aphasia

• paraphasias common

• global aphasia: usually damage to both Broca’s and Wernicke’s area

• paraphasia: substitutes words with incorrect word or sound

18

Thursday, April 21, 2016

• wrong phonemes

• conduction aphasia: difficulty in repeating, produce unintended sounds • damage to arcuate fasciculus (connection between Wernicke’s and Broca’s) • paraphasias common

• agraphia: specific impairment in writing

• usually associated with issues in Broca’s area

• alexia: impaired reading

• usually associated with issues in Broca’s area

• anomia: difficulty with names

• usually associated with damage to Wernicke’s area

• supramarginal region

• circuits:

• speaking a heard word: motor output form auditory input

• first activate primary auditory cortex to process sound

• goes to Wernicke’s area for comprehension of word

• then goes to Broca’s area via arcuate fasciculate (between superior temporal and  inferior frontal) for processing/planning motor output

• finally goes to motor cortex to say the word

• speaking written word

• goes through VI and rest of visual areas

• goes to angular gyrus

• to Wernicke’s

• to Broca’s

• to motor cortex

• passively viewing words: brain activity only in visual processing areas (occipital cortex) • passively listening to words: brain activity in primary auditory areas

• when people asked to speak word after viewing: brain activity in motor areas only • NOT Broca's

• when asked to generate new word associated with language processing: NOW Broca’s area  active

• coming up with appropriate words, plan for motor output  

• dyslexia:

• planum temporale:  

• people without dyslexia: left is much larger

• with dyslexia: symmetrical hemispheres

• ectopias: abnormal development of cells in the wrong places

• cluster of cell bodies  

• polygri: small abnormal invaginations

• cortical disorganization occurs mostly during development

• acquired dyslexia: result of some sort of damage

• people learn initially to read

• deep dyslexia: substitution errors of related words (ex: process “horse” as “cow”) • issues with reading abstraction

• hard to discern subtle word differences

• surface dyslexia: people fine with most parts of reading

• have difficulties with sounds of certain letters

• problems with irregular use of words (ex: tough, dough have different sounds with  same letters)

19

Thursday, April 21, 2016

• decreases activity in left inferior frontal regions, parieto-temporal fusiform face areas when  asked to perform phonemic activity (rhyming words)

• patients with damage to temporo-occipital regions

• able to copy portrait well, but struggle with drawing from memory

• details missing, face is gone

• less issues with sensory and motor - can draw from example

• connection between stored representation is an issue

• drew the wrong things

• unilateral object agnosia (tumor in right parieto-occipital region)

• completely unaware of one side of the visual field

• will draw people with only one arm

• NOT a visual processing issue - but attentional awareness

• issues with occipital region:

• shown a face - don’t recognize (strange handwriting)

• attentional mechanisms: optic agnosia (in occipital region)

• can determine window frame drawing, but when line/squiggle drawn through it, they  cannot distinguish what it is

• cannot dissociate figure from ground, or other overlapping lines

• sometimes, can separate straight lines, but can’t make it out when there are curved lines  over it

• left premotor area:

• damage: deficit in inhibition (motor output) - impulsive movements in drawing and writing • when asked to draw circle, draw multiple

• when asked to draw square - draw squiggles

• cannot write numbers

• “I noticed that something was wrong, but couldn’t alter it”

• frontal lobe lesions:

• damage results in issues with serial tasks

• can draw single figures (copying and from memory)

• however, once there are more figures in the row they can’t do anything

• dorsal stream: parietal

• “where” - locations

• ventral stream: temporal

• “what” - visual processing/attention

Hemispheric Asymmetry  

• hemispheric specialization/lateralization of functions

• motor pathways from one hemisphere have strong contralateral projection managing proximal  and distal muscles

• ipsilateral projections not strong - only involved in proximal responses

• cutting corpus callosum is a treatment for debilitating seizures

• split-brain patients - still retained same IQ

• now info from left visual field ONLY goes to left hemisphere (same for right) • hemispheres are ignorant of what the others have learned

• Sperry experiments: stimuli directed to either hemisphere

• project words to either hemisphere by showing in one visual field

20

Thursday, April 21, 2016

• words projected to left hemisphere had language capabilities - those to the right  hemisphere had no linguistic capabilities

• left more involved with vocal and grammar

• right hemisphere can recognize simple words and process emotional content • testing split brain individual with non-verbal stimulus

• show normal person key in their left visual field - can verbalize “key”

• split brained person shown key in left visual field

• crosses to right visual cortex via subcortical visual pathways (independent of corpus  callosum)

• visual areas can’t communicate with language parts of left

• —> verbal responses impossible - can’t verbalize what they see

• if key shown in right visual field - seen by left eye

• goes to left visual cortex

• CAN verbalize because doesn’t need to cross corpus callosum

• left hemisphere doesn’t know what the left hand is doing - completely controlled by right  hemisphere

• hemispheres process info different in normal humans

• right ear advantage

• dichotic presentation - giving different sounds to the 2 ears

• when conflicting info goes to both ears, info to the right ear reaches Wernicke’s  area first - subject repeats only right ear information

• right handed people identify stimuli from right ear more accurately (only 50% of the  reverse in left handed people)

• may be due to preferential connection between right ear and left hemisphere • if presented to ears at separate times, this no longer holds (monoaural presentation) • visual perception of linguistic stimuli

• tachistoscope test: stimuli presented to either left or right visual field

• if short enough, only goes to one hemisphere (contralateral)

• verbal stimuli (words and letters) better when going to left hemisphere

• nonverbal (faces/shapes) better when going to right

• planum temporale (auditory region)  

• upper temporal lobe

• larger in left  

• part of Wernicke’s area

• in musicians, left planum temporal larger than non-musicians (asymmetry more distinct) • Broca’s area larger on the left

• auditory regions of right hemisphere play major role in music perception • perception of music impaired by damage to right hemisphere

• music activates right more

• EXCEPTION: perfect pitch involves left (bc involves verbal and musical ability) • these are generalizations - can’t assign perception of speech and pitch to left and music to  right (collaborate with specializations)

• prosody: perception of emotional tone-of-voice components of language • right hemisphere

left

right

phonetic

nonlinguistic

sequential

holistic

21

Thursday, April 21, 2016

left

right

analytical

synthetic

propositional

gestalt

discrete temporal analysis

form perception

linguistic

spatial

• possibly evolved from differential limb use for routine tasks

• experiment 1: split-brain subject asked to use left hand to pick object on left visual field (right  hemisphere)

• chooses spoon with left hand because right hemisphere sees the spoon • experiment 2: each field shown different object (left - spoon, right - pencil) and subject asked  to use both hands to pick up the object seen

• right and left hands DON’T AGREE - may each pick up a different object, or right hand (left  hemisphere) may actually prevent the left from performing

• conclusion: each hemisphere can respond independently

• left hemisphere may dominate even if nonverbal response

• experiment 3: subject asked to arrange blocks to duplicate pattern shown on card • CAN’T do it with right hand (left hemisphere)

• can do it with left hand (right hemisphere) —> right hemisphere can process visuospatially  better

• experiment 4: subjects shown 2 figures (one in each visual field) - asked to draw stimuli with  both hands simultaneously

• normal people: can do it if identical stimuli or mirror reversed stimuli

• cannot do it if incompatible spatial maps

• split-brain patients: much better performance - able to carry out conflicting motor programs • spatial representation of movements are maintained and isolated to separate  hemispheres

• lateral specialization in both hemisphere may come from unilateral mutations to one  hemisphere

• left gives up capacity for perceptual groupings to accommodate language development • no overall cost to cognitive system due to connections with corpus callosum • illusory contours (when you see a border that isn’t there)

• both hemispheres can tell whether perceived shape is fat or thin

• when outlines actually drawn, only right hemisphere can still tell the difference • mnemonic functions:

• left: semantic processing (flow charts)

• right: episodic memory (date on calendar)

• patient VJ: split brain

• could speak material given to left hemisphere (not right)

• can’t write words given to left hemisphere, but COULD write words given to right  hemisphere

• —> intact phonological system NOT prerequisite for writing

• patient PS

• left brain tries to interpret actions of both hemispheres (tries to make up for split brain) • chicken claw shown to left hemisphere, snow shown to right

22

Thursday, April 21, 2016

• given 8 picture choices - told to pick related pictures

• left hand chose snow shovel (right hemisphere)

• right hand chose chicken (left hemisphere)

• when asked why he picked those two, said “chicken claw goes with chicken, and you need  a shovel to clean the chicken shed”

• can’t verbalize what he saw with the right hemisphere (left eye)

• deficits in spatial perception after damage to right hemisphere (especially in parietal and  temporal)

• astereognosia: cannot identify objects by touch

• prosopagnosia: can’t recognize faces (mainly due to right hemisphere - fusiform gyrus  between occipital and temporal lobes)

• developmental and acquired

Research - language

• dyslexic: connectivity issues

• tractography study in dyslexia: neuroanatomic correlates of orthographic, phonological and  speech processing

• irregular words are cognitively processed more slowly

• orthographic: written word

• phonological: heard word

• indirect:

• grapheme - phoneme conversion root

• have to cognitively process - think more about rules

• direct lexical root: for more frequent words (learned associations)

• no real cognitive processing (simply association)

• neural roots associated with reading:

• dorsal root: temporoparietal

• sounds (phonological awareness)

• ventral root: occipito-temporal

• grapheme, orthography (written words)

• both areas show decreased activity in dyslexics vs. regular readers

• arcuate fasciculus: connects left temporal parietal and left inferior frontal gyrus • connects Broca’s and Wernicke’s

• assumed that left arcuate involved in dyslexia

• hypothesis:

• difference in left arcuate fasciculus in dyslexics

• possible differences in left inferior fronto-occipital fasciculus

• may connect left ventral occipitotemporal (new possible reading area)

• difference between areas involved in phonological (word sounds) and orthographic (visual)  components of dyslexia

• difference between radial and axial diffusion (what is the nature of this difference?) • differences in speed of conduction and processing

• structural MRI technique showing CONNECTIONS

• allows reconstruction and assessment of white matter tracts (connecting brain areas) • fractional anisotropy gives high resolution method of studying fiber systems and  connectivity/circuitry

• doesn’t measure connections

23

Thursday, April 21, 2016

• computer reconstruction of connectivity based on probability

• anisotropy: does not diffuse equally in all directions

• measuring diffusion of water inside the axons

• water is constrained - goes along a specific path

• fractional anisotropy is scalar value from 0-1, describing degree of anisotropy • 0: totally isotropic

• 1: diffusion occurs ONLY on one axis, fully restricted in all other directions • computer model based on the levels of anisotropy

• reflects density, axonal diameter and myelination

• can measure axon 2 ways

• radial diffusivity: related to myelination

• diffusion down the length of the axon: tells more about the axon itself

• study: 20 dyslexics and 20 regular adults

• normal range of non-verbal IQ

• dyslexic readers had issues with word reading, pseudo-word reading and spelling • tested phoneme awareness

• phoneme deletion task: shown non-word and asked to delete one of the phonemes  (ex: norf —> nor)

• spoonerisms: swap initial phonemes of 2 words

• tested speech-in-noise

• constant background noise; asked to identify particular words in different decibels • finds threshold of detection of word against noise

• orthographic processing

• words presented really quickly, asked if it was spelled correctly or incorrectly • correlational study: measuring both brain and behavior in two groups, seeing if there are  relationships

• results:  

• dyslexics showed decreased fractional anisotropy in overall left arcuate (between posterior  temporal and frontal)

• more isotropic

• decrease in RADIAL diffusivity, no difference in axial diffusivity

• from this, we conclude that changes NOT due to changes in the axon, but issues  with myelination of neurons

• the neurons themselves are the same

• explained by differences in DIRECT connection in arcuate fasciculus (no significant  anterior/posterior differences)

• no differences in right arcuate fasciculus

• no group differences in left inferior fronto-occipital fasciculus

• left arcuate fasciculus DIRECT involved in phoneme awareness and speech perception • area that explained most of the group differences

• phonological processing related to the size of the left arcuate fasciculus • nothing to do with orthography

• left inferior fronto-temporal fasciculus correlated with orthography (no group differences) • found in correlational study

• nothing to do with phoneme awareness

• making orthographic decisions about words related to thickness of inferior fronto occipital fasciculus

• in dyslexic readers, likely difference in both phonological and orthographic processing • ventral root processes orthographic properties

24

Thursday, April 21, 2016

• dorsal root (with arcuate) more related to phoneme awareness

• double dissociation between orthography and phonemic processing

• conclusion—> dyslexia associated with differences in:

• processing (behavior)

• phonological processing

• orthographic processing

• brain regions

• dorsal root - left arcuate fasciculus (involved in phonological processing) • group difference

• correlational differences in left inferior fronto-occipital

25

Page Expired
5off
It looks like your free minutes have expired! Lucky for you we have all the content you need, just sign up here