PSC 137 Exam 1
Autonoetic consciousness
remembering that involves the mental re enactment of previous events at which one was present (recall or recollection) exactly what the hippocampus is doing int he brain
Noam chomsky
reinforcement cannot explain how verbal language is learned (denies BF skinners ideas about how language is learned) humans must have a genetic predisposition to develop language
karl lashley (1950)
-prominent American psychologist -wanted to find the specific location of memory in the brain -is memory localized? behavior movement is popular during this time experiments -trained rats to navigate mazes -made lesions and knife cuts of varying sizes in different parts of the cortex (can i damage a specific part of the brain and the animals wont remember what was taught)
episodic memory
Autobiographical memory for information of personal importance.
reinforcement learning
BF Skinner press lever for food used reinforcement schedules animals would press lever the most under variable ratio schedule of reinforcement -has to make response a certain amount of times, but the number varies from trial to trial, so the animal knows it has to respond if it wants food if you stop giving animals food, they will keep pressing because they think eventually they will get food (most resistance for extinction) perfect for gambling -we keep playing even after long periods because we think we will get money eventually CS (tone) US (Puff of air)-> UR (eyeblink) then after conditioning: CS (tone) *association* US (puff of air -> CR (eyeblink)
what is the hippocampus
cortical structure -means it has layers not neocortex -neocortex's have six layers but it only has 3 called allocortex or archicortex -has 3 layers
John B watson
Behaviorist -wanted psych to be a natural science like physics or biology we cant measure abstract things so focus on behavior because it CAN be measured introspection cant help us understand behavior we need to study how the environment and individuals experiences alter behavior the environment and learning are the main things that control behavior -learning becomes a focus in psych departments
the hippocampus and long term potentiation
Bliss and Lomo (1973) put stimulating electrode into perforant path and also put a recording electrode in the dentate gyrus delivered a weak stimulus to PP, you get a weak response in the DG they then stimulate strongly, and get a strong response they then gave a weak stimulus again. the gradual cells then gave a higher response -called this long term potentiation (LTP)
hippocampus proper
CA1 CA2 CA3 "cornu ammonis" (ammons horn)
pavlovian conditioning
CS-> US (bell-> food) - if paired enough, the CS produces a CR (conditioned response)
animal models
Cant measure declarative memory in animals develop tasks that capture features of human amnesia use these tasks to study. the brain regions and cellular mechanisms that give rise to memory Scoville and Milner 1957 -Duplicate H.M.'s lesion, find long-term memory deficit
process of hippocampus
Ec (entorhinal cortex) sends axons perforate through the white matter which goes to the dentate gyrus which sends to CA3 then sends to CA1 which then goes back out to the sibiculum and then sends it back to the entorhinal cortex (EC)
in contrast to lashleys conclusions, Patient HM and EP suggest that
HM and EP suggest that specific types of memories are localized in the brain declarative memories are encoded by the hippocampus not all types of memory are stored in the hippocampus skill learning, perceptual learning etc are encoded by other parts of the brain this understanding led to the multiple memory systems perspective
the hippocampus and memory
HM had damage to many different brain areas -amygdala, entorhinal cortex, perirhinal cortex how do we know his amnesia is due to hippocampus. damage? -need to examine other amnesic patients
Can We Reconcile the Declarative Memory and Spatial Navigation Views on Hippocampal Function? POSSIBILITIES
Hippocampus does different things in humans and animals: -it primarily encodes space in animals and evolved to encode episodic memory in humans (what, when, where) Hippocampus does similar things in humans and animals: -encodes spatiotemporal relationships between stimuli which can be used for spatial memory or episodic memory
how does LTP happen? the chemical basis of LTP: Ionotropic receptors
Ionotropic receptors are located in the plasma membrane. When a neurotransmitter binds to the receptor, the channel or pore opens and allows ions to enter the cell.
LTD-> memory gone-> LTP-> can you bring memory back?
LTD-> memory gone-> LTP-> can you bring memory back?
can this memory be erased by reversing LTP? (last slide cont)
Long term depression -opposite of LTP -depress the synapses -low frequency stimulation for a prolonged period- so the synapses become weaker you can reverse LTP by inducing LTD in the same pathway -LTD can be used to undo the potentiation that you induced you trained the animals and that induced LTP, so what if we go in and give low stimulation which would then reverse the LTP they once established -will giving LTD erase the fear memory stim-shock pairings-> induce LTD in the. same place they did the stim-> test memory RESULTS the fear memory was gone after doing LTD
Associative or Hebbian LTP
NMDA receptor allows cells to increase the strength of their connections Requires glutamate release (glutamate comes from pre-synaptic activity) requires depolarization (post-synaptic activity) known as Hebbian plasticity- "cells that fire together wire together" -if neurons that were firing together strengthen their connections, the. brain can use this to produce learning and memory
how can cells tell if they are firing together?
NMDAR activation requires two events (the R stands for receptor) these events are indicators that pre and post-synaptic cells are both active at the same time glutamate= pre (tells us that presynaptic neuron is active) depolarization= post (tells us that the postsynaptic neuron is active) Serves as a coincidence detector -when pre and post synaptic activity happen at the same time, the NMDA is a detector of this and allows calcium to flood in -If two events co-occur then it becomes active and allows the synapse to become plastic
Understanding Field Potentials: Postsynaptic Potential
Postsynaptic current causes excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell..
Double dissociation of conditioning and declarative. knowledge relative to the amygdala and hippocampus in humans (Research article). RESULTS
SM046 (amygdala damage) -no fear response WC1606 (hippocampal damage) -fear to screen that are paired with boat horn -BUT dont remember anything. after RH1951 (hippocampus and amygdala damage) -no fear of screen -dont remember what happened in the room Galvanic skin response (response to US) -Controls show a UR and a CR -Amygdala patients show a UR but no CR -Suggests the boat horn scares them but they can't learn to be scared of the CS -Hippocampus patients show UR and CR CONCLUSIONS -Single experiences consist of multiple elements -The hippocampus encodes the declarative aspects -The amygdala encodes the emotional aspects -Can have an emotional memory even though you don't remember the experience (non-declarative)
Can we modify a memory that the animal already has? -Can we get animals to fear a place where nothing bad has ever happened? Creating a false memory in the hippocampus
Tag neurons that were active when the animal was exploring a new place -(Doxycycline is removed) -exploring context A where nothing bad happens- they just form a memory here put animals back on doxycycline (no more channelrhodopsin/ ChR2) then put animals in context B- receive foot shocks here. right before each footshock, they stimulate the cells that encoded context A. they are making the animals think about context A right before they get shocked in context B -can you create a memory that context A is actually bad they then put animals back in context A for test as a control, they put animals in context C (just to show they dont freeze in every context) RESULTS not scared in context A at first but then after context B, when they are put back in context A they are now scared of A, and they are not scared of C -the freezing that is observed in A is specific to this context -they can create a fear memory that never actually happened
cognitive revolution
The shift away from strict behaviorism, begun in the 1950s, characterized by renewed interest in fundamental problems of consciousness and internal mental processes. criticism of behaviorist ideas
Patient E.P
Viral encephalitis which caused selective damage to medial temporal lobe on. both sides and the hippocampus on both sides anterograde and retrograde amnesia for declarative memories intact non declarative memories but. impaired declarative memories
multiple memory systems
a complete understanding of memory can only be achieved by recognizing that the content of experience is important memories are segregated into different brain. regions according. to their content these ideas are the central premises of what is called the multiple memory system perspective
understanding field potentials: structure and function of neurons
a neuron is composed of a cell body (which contains the nucleus), dendrites, an axon, and axon terminals
damage to hippocampus produces
a selective loss of declarative memory
excitatory postsynaptic potential (EPSP)
a slight depolarization of a postsynaptic cell, bringing the membrane potential of that cell closer to the threshold for an action potential
the general goal of psychology
a. derive a set of empirical principles that describe how variation in experience influences behavior (behaviorist) b. provide a theoretical account that can explain the observed facts
patient WH
alcohol abuse and heart attack -bilateral damage to HPC peririhinal. cortex and amygdala were intact, some cell loss in the entorhinal cortex anterograde and severe retrograde amnesia
Patient LM
alcohol abuse and seizures -had bilateral HPC damage -peririhinal. cortex and amygdala were intact, some cell loss in the entorhinal cortex anterograde and less severe retrograde amnesia
ionotropic glutamate receptors
major excitatory neurotransmitter 2 kinds of glutamate receptors: -AMPA: when it binds glutamate it will let Na+ into postsynaptic cell -NMDA- lets Na+ in as well as Ca2 when it binds to glutamate. for LTP, you have to activate NMDA
Can we use modern neuroscience tools to erase and reinstate memories? engineering a memory with LTD and LTP
auditory information comes into thalamus which is sent to the lateral nucleus of the amygdala during conditioning, the tone is paired with the footshock which drives learning (freezing) the tone information coming in from the thalamus. comes in at the same time as. the. footshock stimulation- so its thought. that pairing the auditory information with the footshock induces LTP ( a potentiation of CS pathway) which then drives freezing STUDY did experiement with 2 groups of rats first group: a tone was presented and paired with shock second group: stimulated auditory input to the lateral amygdala instead of presenting animals with the tone- their paired stimulation of this pathway with the footshock wanted to show that animals could freeze to stimulation of the brain area just as they would with the actual auditory cue RESULTS the animals did learn they measured lever presses rather than freezing (the stimuli would stop them from pressing the lever- because they are scared) tone-shock group: when. tone comes on, they immediately stop pressing lever stim-shock group: they stop lever pressing and freeze when the stimulus happens so yes, they can use artificial stimulation to induce freezing behavior
Noetic consciousness
awareness of the past that is limited to feelings of familiarity and knowing (the KNOW judgements) mediated by the. perirhnal cortex
do place cells exist in other animals
bats study -found 3D place cells in bats -
perceptual memories
bike-> car -> bike you dont have to be aware of seeing the word bike to read it the second time faster
summary of modern tools for memory
can induce or prevent the retrieval of a specific memory with optogenetics can erase a memory with LTD and then reinstate it with LTP can create a fear memory when animals are awake -can create a rewarding memory when animals are asleep
Double dissociation of conditioning and declarative. knowledge relative to the amygdala and hippocampus in humans (Research article) memory systems
in humans, declarative memory requires the hippocampus in animals, emotional memory requires the amygdala Patient groups -SM046: bilateral damage to amygdala (urbach-wiethe disease -WCI606: damage to hippocampus (heart attack) -RH1951: damage to both hippocampus and amygadala (encephalitis) used fear conditioning Memory measures -galvanic skin response= emotional CR -questions. about experience= declarative memory
lashley's principles
mass action equipotentiality
is the hippocampus REQUIRED for spatial learning? -radial arm maze task
choice phase -3 doors are open, so rat goes into them to get food win-shift phase -opens all eight doors BUT only puts food in the doors that were NOT open in the choice phase damaged inputs and outputs of the hippocampus because it will mess up hippocampal function before lesions, the rat performs well. When he damages the parts of the hippocampus, they do not do well on the task how do you know spatial learning is impaired? -test animals on a version. of the task that does not require spatial memory -design task that require the same motivation, motor skills and sensory processing but does not require spatial memory
non spatial version of radial arm maze task -cued version
choice phase -four doors are open, but there are lights on it and gets food in the open. doors win-stay phase -all arms are open -only four arms have lights on -doesnt matter if the rat previously went to them or not, they just have to follow the light to get food -so ignore spatial cues and doesnt have to remember the arms they previously went to with hippocampal lesion, this task doesnt affect them because they just have to follow the light
declarative memory
conscious explicit memories we are consious and aware of two types of declarative memory
hippocampus dependent learning tasks
context fear conditioning trace conditioning
two types of tone conditioning
delay conditioning- tone turns on and when the tone turns off the foot shock turns on -there is a delay -does not require hippocampus trace conditioning- turn tone on and turn it off, and then wait a period of time and then deliver the shock -does require hippocampus -in order to associate tone with shock, the animal must continuously think about the tone and then gets shocked (so animals must maintain a memory during the interval- you need the hippocmapus to maintain the memory for the. tone) you need hippocampus for place learning, but also need it for. trace conditioning which does not have spatial component -also true for humans, not just mice! for humans they did eyeblink conditioning in amnesic patients -puff of air into eye instead of shock and. measure the blink -pay attention to movie and the auditory cue will go on and go off. and then later will receive a puff of air in eye -delay: normal in amnesic patients -trace conditioning: amnesic patients are significantly impaired in learning to blink
does damage to the hippocampus affect spatial memory?
developed virtual version of water maze task patients with damage to the hippocampus wander around in big loops because they dont know where the platform is
knowing vs remembering
edlridge and knowlton, 2000 fmri study subjects studied word list recognition test 20 minutes later was this word on the list? do you remember (R) or just know (K) when youre using a sense of familiarity, the hippocampus is not active but when you remember, the hippocampus is active monkeys without hippocampus can use familiarity to solve the DNMS task -not a great model for episodic memory deficit displayed by HM, but was great for determining familiarity Patient EP also had damage to perhirinal cortex which is why he couldnt remember the words in the word tasks
major input of hippocampus proper
entorhinal cortex -perforant path -integrated cortical information -no unimodal information (no single type of sensory info that goes directly to the hippocampus. it is first integrated into other parts of the cortex first) -only polymodal information neocortex-> entorhinal cortex-> hippocampus highly integrated information goes into the entorhinal cortex and then into the hippocampus
hippocampus pathway
entorhinal cortex-> dentate gyrus-> CA3 pyramidal cells-> CA1 Pyramidal cells Perforant path: pathway from entorhinal cortex to dentate gyrus mossy fibers: path from dentate gyrus to CA3 pyramidal cells schaffer collaterals: CA3 pyramidal cells to CA1 pyramidal cells
two types of declarative memory
episodic and semantic memory
The Chemical Basis of LTP: Antagonizing NMDA receptors block the induction of LTP, not the expression of LTP
establish baseline then give strong stimulus then give. weak stimulus and you see LTP when the NMDA receptor is blocked, you give strong stimulus, and then you give weak stimulus, there is no LTP, instead it goes back to. what it was before Conclusion: the NMDA receptor is needed to induce LTP what happens if you induce LTP. and then block NMDA receptors? -it doesnt have an effect -NMDA is not necessary. to. EXPRESS LTP -NMDA is necessary to INDUCE LTP, but once LTP has already. happened then you dont need it anymore to EXPRESS LTP
cognitive maps
ex. rat put in plus maze. taught rat that the food is on the right. what did the rat learn to do? -Behaviorists say that the rat learned stimulus response association with this place and food- when the rat is reinforced with food on the right, it learns to make a right to get the food -tolman's cognitive map: would say that rats learn the spatial location of the food (food is in the east corner). how do you test which one it is? -does the rat turn right or go to the east? trained rat to turn right in the maze -put rat on the other side of the maze. will it turn to the right or left? -the rat actually went to the left because it knew the spacial location (went east)
water maze task (spatial version) (hidden)
find hidden platform to get out of the water because they cant see the platform, they. have to learn where in space the platform is how quickly does the rat get to the platform -once the rat learns the spatial location of the platform, they go over to the platform instantly by the end of the training, the researchers take the platform out rats use spatial strategy -they search in the same place that they were trained it was at with hippocampal lesion, they dont know where the platform is so they swim in circles -they do not have spatial memory is it distal cues that control behavior? -stripes on one side, triangle on the other side -learn to swim toward the platform which is by the striped cue -now leave platform where it is, but move cues -yes the animal's search rotates with the distal cues -THIS IS AN EXAMPLE OF WHAT PLACE CELLS DO
retrograde amnesia is more pronounced
for recently formed memories Older memories often remain intact
do humans have place cells
found hippocampal neurons that look like place cells looked at epileptic patients virtual navigation -make sessions as realistic as possible
choosing the test and inducing stimuli
give weak stimulus to axons and record the EPSP -do this over and over to get a baseline -baseline will always be around 100 then give strong response and theres a huge increase then. give a weak stimulus again, you get a response that is 150% bigger than the first weak response weak, strong, weak
fear conditioning for doubled dissociation study
green, blue, yellow, or red color flashes when the blue screen flashes, a loud noise comes on blue screen= CS
chicken sexing example
had no conscious awareness of knowing how they were determining if the chick was male or female but they did so with 95% accuracy
hippocampus formation
hippocampus proper dentate gyrus subiculum entorhinal cortex
trace conditioning and awareness
if you are aware of the stimuli, then it will help you learn- which you need the hippocampus for created awareness for the tone and the puff of air delay conditioning: they learned even if they werent aware of the tone and puff of air trace conditioning: being aware made their memory better. if they were unaware, they. did. worse conclusion - HPC is related to trace conditioning because it involves awareness and explicit memory
LTP
increase in the. strength of synaptic response as a result of stimulation in vivo- in the living (whole animal) in vitro- within the glass (brain slice) -place stimulating. electrong in shaffer collaterals -place recording electrode in CA1 to record LTP
learning and memory are theoretical concepts
infer the existence of learning and memory based on change in behaviors
damage to the entorhinal cortex, perhirhinal cortex or the amygdala is
is not required for amnesia to be observed
Patient GD
ischemic episode -had bilateral HPC damage the entorhinal cortex, perirhinal cortex, and amygdala were intact the patient still had anterograde and retrograde amnesia
mirror learning task
learning to trace an image through looking at it in a mirror HM learned this task quickly and could remember it across days -but when asked if he had learned this before he would say no- no declarative knowledge of the experience
Where is the hippocampus
located in the forebrain in the temporal lobe, more specifically in the medial temporal lobe shaped like a seahorse
experiment with rat and wells -behavioral decoding experiment place cells tell us what? SPW tell us what?
maze with holes around the maze in a grid pattern. the experimenters put food in some of those wells. the rat starts in the middle and has to. wander around to see where the food is located. after it finds the food, he has to go back to the middle, and when he goes back to the middle it will get another piece of food. What does this study tell us?? the hippocmapus encodes an animals past present and futue locations place cells tell. present sharp wave ripples play the past during those sharp wave ripples they can play future paths as well
semantic memories
memories that you are aware of facts you just know the information -they may have started as episodic memories but change into semantic because you do not know when or where you learned it they. do not have the autobiographical component
lashley's conclusions
memory is not localized the size of the lesion had the greatest. effect on a rats ability to remember how to navigate the maze the location of the lesion did not matter
procedural memories
motor memories learning how to do something
HM's amnesia
motor skill, learning, perceptual learning, and priming were intact HM had no memory of learning these tasks had normal non declarative memory but no declarative knowledge
cognition, behavior and the brain
mouse and monkey brain appear different from human brains but have many of the same structures and architecture made of same material -neurons synapses ect
context fear conditioning
mouse explores tone comes on, never heard it before the tone is the conditioned stimulus shock is then paired with the tone the shock is the unconditioned stimulus pair the tone and shock a few times -when the tone comes on, the mouse will then freeze which is called the conditioned response -the context also makes the mouse scared. so the place the mouse is in is a conditioned stimulus as well
psychologists who study the brain
neuropsychology -individual who study human patients who have brain damage or a clinical disorder cognitive neuroscience -studying intact human brains behavioral neuroscience -study animals brains
non declarative memory
non-conscious and implicit procedural, perceptual, or emotional memories
Damage to the hippocampus does not affect
non-declarative memory
memory
refers to the persistence of learning in a state that can be revealed at a later time
challenges to lashley
patient HM -damage to medial temporal lobes including hippocampus -had amnesia for episodic memories eyeblink conditioning -rabbits hear noise and get a puff of air in eye so every time they would hear the noise they would blink -localized in cerebellum
william scoville
performed experimental operation and removed operation and removed HM's hippocampus Seizures were reduced but the surgery also produced profound (and unexpected) memory loss
delayed non-match to sample (DNMS) (mortimer Mishin)
picks up object and puts it back down. then wait (delay period) then doors open back up and there are two objects, one they saw before and one they havent seen. The monkey is supposed to pick the object they havent seen and they will find food under the novel object
LTP experiment
place stimulating electrode by schaffer collaterals extracellular recording electrode placed at CA1 pyramidal cell does stimulating. the shaffer collaterals make CA1 more positive? -
non spatial water maze task (cued)
platform sticks up out of the water so the rats can see the platform dont have to use spatial cues -they just have to see it and swim right towards it
toulmin experiment ex
put rat in complicated maze and has to get the food trained 3 different groups: -group 1 always gets reward -group 2 never gets reward -group 3 gets reward on trial 11 according to behaviorists the results will be: -group 1 will learn best -group 2 will never learn -group 3 will perform half as strong as group 1 toulmin says -group 1 will learn fastest -group 2 wont learn anything -group 3 will learn very quickly after trial 11 results: -group 2 doesnt learn -group 3 learned quickly after trial 11 -group 1 learned from the start the cognitive map is located in the hippocampus
what does the hippocampus do in rodents
put recording electrode into the hippocampus in rodent and listened to the neurons in the hippocampus while they were walking around -what makes the hippocampal neurons active when they are walking around? put 4 electrodes very close together in the hippocampus- he picked up action potentials with this so he could isolate the response of individual neurons -discovers place cells
memory tests
recognition -familiarity: seems familiar but dont know who they are. (measure familiarity by knowing. have you seen this word, and if you feel like you know youve seen it, then classified as know) -recollection: recognize person, and all info about person comes to mind (if you remember where you seen it, this is classified as remember) recall both recollection and recall uses the hippocampus in recognition, familiarity uses the perirhinal cortex NOT the hippocampus -word lists
synaptic plasticity
reduced preparations LTP changes these connections between neurons in the brain
Robust learning of affective trait associations with faces when the hippocampus is damaged, but not when the amygdala and temporal pole are damaged (STUDY)
show picture of man - say kevin talked behind the back of his best friend showed picture again - how much do you trust this person RESULTS -intact: remembered faces and learned emotion -HPC damage: could not remember faces but did learn emotion -HPC and AMYG damage: could not remember faces or learned emotion
major output of hippocampus proper
sibiculum gets info from the hippocampus and it sends it back to the entorhinal cortex subcortical-> emotional structures
Features of DNMS
similar to word list learning normal rule acquisition (Cognitive function) Normal short term memory impaired long term memory CONCLUSION (from DNMS STUDY) if you damage just the rhinal cortex, you get amnesia- just like HM, but this is not correct. remember: Multiple memory systems -the context of memory is critical -need to know what is being learned and remembers -animals and people can solve the same task using different strategies -ex. horse learning math problems: 2+4? would stomp foot 6 times and would get reinforced. BUT the horse used the body language of trainer to know when to stop stomping its foot.
galvanic skin response
skin conductance correlated with emotional responding lie detector test
history of psychology
started as the study of the HUMAN mind -the human mind is different enough from other organisms to need to study it separately rene descartes -humans are made of a material body and an inmaterial mind- cartesian dualism -the human mind is not completely biological -animals only have biology the mind IS completely biological charles darwin -origin of species book -animals and humans have shared ancestors and characteristics -if the human brain is biological, then we can share parts of it with animals -we can study animal brains and learn things about the human brain -psychology then switched to the study of the ANIMAL mind John B Watson -study of BEHAVIOR
Intrinsic Circuitry
trisynaptic loop -entorhinal cortex to dentate gyrus -dentate gyrus to CA3 -CA3 to CA1 EC into DG (via pathway called Perferant path {PP}) then to CA3 (second synapse) then to CA1 (third synapse) via. the SC (schaffer collaterals?)
history of the study of the brain
study of human mind-> science of behavior-> science of cognition-> science of the brain
how to study human cognition
study people -using cognitive tasks study animals -called comparative cognition
stimulus response learning
the ability to learn to perform a particular behavior when a particular stimulus is present
equipotentiality
the effect of a lesion on memory is independent of its location memories can be stored anywhere, any part of the brain can encode memory
mass action
the more tissue removed the greater the memory impairment
learning
the process of acquiring new information a relatively permanent change in the processes underlying behavior that results from experience -a change in behavior is necessary to say that learning has occurred -the change in behavior has to be relatively permanent -has to result from experience (ex. palmar reflex- babies havent learned to grab finger, but does so reflexively) -we have to infer that learning exists- the behavior itself is what we see because of the learning LEARNING DOES NOT EQUAL PERFORMANCE -ex. test anxiety
the search for the engram (search for memory in the brain) what is an engram
the set of physical processes and changes in the brain that forms the basis of a memory it is also called the memory trace
comparative cognition
the study of the development of cognitive abilities across species and the continuity of abilities from nonhuman to human animals -humans and animals share similar cognitive processes -ex. reinforcement learning -most studies come from animal studies often divided into two different researchers -human researchers -animal researchers
Does context fear depend on the hippocampus like other spatial learning tasks?
they trained (learned to fear the tone and the context) animals and then made lesions in the hippocampus and gave them a test context+tone=shock -then lesion after 1 day, 7 days, 14, or 28 days (removing the hpc when memories are new or memories are old) test memory of tone -put. mouse in novel environment and see if scared of tone test memory of context -put mouse in the same context that they ere trained and see if they freeze RESULTS -day 1 lesion; context fear: spend time freezing- aka they learned to be scared of context. once the HPC is lesioned, they do not freeze at all- so you can completely get rid of context fear -day. 1 HPC lesion tone fear: Fear to the tone does not change, they a re still afraid of the tone. -context fear for 28 day lesion- the longer they waited the less effective the HPC lesion was -context fear for 28 day lesion: hippocampus never plays a role in tone fear Hippocampus is involved in context fear. They still are afraid of the tone, but not the context.
how to study hippocampal plasticity
use reduced preparations -brain slices -remove hippocampus from rat and take a slice through it and use the slice to study the way that the neurons in the HPC become plastic (aka how they change)
understanding field potentials: membrane potential
voltmeter with. two different recording electrodes- measures two different electrical potentials -if outside neuron then there. is zero potential -if one electrode is placed inside the neuron then we get a. negative potential. -70mv
patient HM (1957)
was in a bike accident and had intractable epilepsy had a brain operation at 27 Brenda Milner performs psych evaluation on HM -found that despite. memory deficit, language skills, IQ, perception, reasoning, ability and motivation were normal -not all memory. was affected -short. term and. working. memory were intact -could not form long term memories or new memories (anterograde amnesia) -lost memories from before the operation (retrograde amnesia) -childhood memories are intact so retrograde amnesia didnt extend back to childhood first pure memory deficit with damage localized to one part of the brain
place cells
when a rat explores a new environment, cells in the hippocampus fire in specific locations -these cells are called place cells -the area where a specific cell fires is called its place field maybe its just sensory cells? -No. place cells are stable in the dark. when the animal is placed in the maze with the lights off, the action potentials still fire in the same place place cells remap in new environments -if in black box it will fire in one area, but if in blue cylinder, the cells will remap and fire somewhere else. theta frequency -oscillation (around 4-10 Hz) that you see when all the cells are firing and you cant tell what cell is what -happens when the rat is walking around -tells where I am in. space right. now SPW -Sharp wave ripples -large bursts of activity that happens when they stop walking -place cells fire in sequence -the frequency is very high -the place cells replay the places in the environment where the rat just was -Where I was
The Chemical Basis of LTP: What Is Special about NMDA Receptors?
when you stimulate weakly, it. will turn on AMPA receptor, but cant turn on NMDA recepetor bc it is blocked by. the Mg2 receptor if you stimulate strongly, then more Na+ comes flooding in, so the positive charge makes the Mg2+ ion release so NMDA receptor can turn on and Ca2+ can come in
c
yes Rewarding stimulation in medial forebrain bundle -if you stimulate the medial forebrain bundle, the rats really liked it. -the rats would lever press to get stimulation of. this area -this is one of the main dopamine pathways in the brain, so it releases dopamine all over the brain STUDY recorded place cells as the rat was running around in the environment they then design a system that detects the firing of a place cell, and the system turns on the stimulator and stimulates the medial forebrain bundle (MFB) when you put rat back into environment the next day, the rate spends all their time in the place field where the place cells fired the day before to get the stimulation of MFB then they do the same thing but during sleep: -picks a place cell, and the animal goes to sleep, and every time the place cell fires during sleep, MFB stimulation is delivered -when the rat wakes up, the rat goes to the area of the environment where the place cells firing happens in that specific environment (remember they never were stimulated in the arena) -so you created a memory that the rat likes this area of the arena -their behavior is directed -the place cell activity has something to do with navigation
evidence of LTP in stim shock group? (last card continued)
yes when took brain slices from the paired vs unpaired animals (paired with shock, vs not paired with shock) paired group: pairing the stimulation and shock potentiates the pathway -induced LTP in this pathway More AMPARs in paired group vs unpaired group -a sign that LTP has occurred in the pathway
changing the membrane potential
you can excite it or inhibit it depolarization: getting more positive. if you. depolarize it enough, the cell will fire an action potential hyperpolarization- making more negative. less likely to fire an action potential in the postsynaptic. neuron resting potential is -70mv