Week 14 - Behavioral Neuroscience
Week 14 - Behavioral Neuroscience PSYC 4183-001
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This 7 page Class Notes was uploaded by Celine Notetaker on Thursday April 28, 2016. The Class Notes belongs to PSYC 4183-001 at University of Arkansas taught by Nathan Parks in Spring 2015. Since its upload, it has received 13 views. For similar materials see Behavioral Neuroscience in Psychlogy at University of Arkansas.
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Date Created: 04/28/16
Week 14 – Behavioral Neuroscience Learning (Continued…) Overview: Cellular Mechanisms of Learning o Long Term Potentiation (+hippocampus LTP) o Glutamate Receptors (AMPA, NMDA) Neural Circuitry of Memory o Medial Temporal Lobe/Hippocampus o Basal Ganglia o Explicit memory & Implicit Memory Cellular Mechanisms of Learning “Cells that fire together Wire together” - Eye Blink conditioning: Changing the way synapses interact by pairing a stimulus (tone) with a reflex (blinking) that has been triggered (puff of air into the eye). o A closer look at the neural form of classical conditioning - The strength of a synapse INC (aka the post-synaptic potential INC) when it fires along with other neurons. Eye Blink Conditioning = Neural model of Classical conditioning (like Pavlov’s dog) - Puffing air at the eye is met with a reflexive blink response - By pairing a tone with the puff of air you can create a synapse between the neuron in the auditory system (of that tone) to the “blink neuron” o Eventually you could cause that person to blink reflexively to that tone even without that puff of air THEREFORE, the strengthening of a synapse = learning If you continued to CO-ACTIVATE the “blink” neuron with the other two neurons you will begin to see GROWTH of dendrites in the “blink” neuron that will connect to Synapse T (in image) and thus we see the STRENGTHENING of that synapse - Learning in the brain is activity dependent Long Term Potentiation (LTP) = Cell Learning *LTP enhances the effectiveness of synaptic transmission via strengthening of synapses (as explained in the eye blink conditioning example) - LTP= The most simplistic representation of Learning in the nervous system - Requires 2 events: The activation of synapses and depolarization of the postsynaptic neuron - LTP can also lead to the formation of new synapses dendritic spines Glutamate Receptors : post synaptic glutamate receptors are KEY to LTP - NMDA: Detects correlated activity o Ionotropic, Ca++ o Induces learning via Calcium (Ca++) - AMPA: Strengthens a synaose o Ionotropic; Na+ o ‘Keeps’ the learning there NMDA - Detect’s the co-activation of the presynaptic and post synaptic neurons o The co-activation must occur at a HIGH/significant rate to be detected - Neurotransmitter Gated AND Voltage Gated Channel - NMDA receptor controls Ca++ channels which is normally blocked by Magnesium o You must have a already depolarized post synaptic cell AND glutamate must be released by the presynaptic cell into the synaptic cleft at the SAME TIME to remove Mg++ and unblock the Ca++ channel o This then allows Ca++ to go through the NMDA receptor (green tube in image) AMPA - Increases strength of synapse Entrance of Ca++ from the NMDA receptor causes the activation of protein kinases o The activation of protein kinases Induces LTP in two ways 1. Increases EPSPs of existing AMPA receptors by having larger currents run through them 2. Inserting new AMPA receptors into the postsynaptic membrane a. = more pores that Na+ can go through Bigger EPSPs LTP in the Hippocampus Paired stimulation 1. Paired stimulation leads to LTP - It can make a cell go from generating NO EPSP to generating a LARGE EPSP o This shows that we are set up with the ability to learn 2. High-frequency stimulation induces LTP a. A “brute-force” type of method b. Sends massive amounts of action potentials down a pathway (50-100Hz) ***Experiment: Inducing LTP while using APV to block the NMDA will cause random sizes of EPSP to be released. This shows that NMDA is critical to the learning process. Preventing NMDA = preventing LTP 3. Low-frequency stimulation of hippocampal pathways leads to long-term depression (LTD) a. Lasting reduction in synaptic strength Smaller EPSPs b. Like forgetting due to the weakening of synapses Used in clinics to decrease activity in areas of the brain that are overactive (depressed patients, bipolar patients, etc…) Artificial Neural Networks - Can be trained a lot like brains do - Mimics LTP in a biological neural networks and applies it to artificial neural networks - The most successful way to train computers to SEE things (for example) o Can also be trained to identify any trend in data Neural Circuity of Memory Engram – A term used to refer to the neural representation or location of a memory - AKA Memory Trace “Where are memories stored in the brain?” Karl Lashley’s Search for the Engram (and failure to find it) - Lashley would train rats to run a maze Then he would start lesioning parts of the rat brain to see if he could find that one part of the brain that totally destroys the ability for them to do that maze, therefore finding the engram o It didn’t work - Instead he found that the proportion of cortex lesioned was associated with the loss of memory rather than the particular regions involved o Larger lesion of cortex = MORE difficulty the rat had in solving the maze **Remember! There is not a single place in the brain where a memory resides, it is distributed across the entire brain Explicit memory Medial temporal lobe and especially the hippocampus is important for forming long term memory Although there is no one storage space for memory there are critical structures for laying down that memory Relational Memory Theory: Poses that the hippocampus forms representations of arbitrary relations among the constituent elements of experience Tying a bunch of stimuli, that were together at the same moment in time, together. Medial temporal Lobe/hippocampus - This and structures within the diencephalon are particularly important for the formation of new long-term declarative and spatial memories. Hippocampus: Receives sensory information Via the rhinal cortex Wilder Penfield’s Experimentation on patients with Electrical Stimulation in the Medial temporal lobe: - Found that when he stimulated a patient in the Medial temporal lobe during a surgery it invoked some of the patients memory o However, it is possible that these could have been hallucinations or an untrue memory - Patient H.M. had portions of his medial temporal lobe removed to alleviate epilepsy o Had extreme anterograde amnesia and partial retrograde amnesia for the years preceding the surgery o He had the feeling of being stuck in time Image: Example of H.M.’s surgery results now lacking the medial temporal lobe Retrograde amnesia = when you lose memories from before the brain trauma/death Anterograde amnesia = when you cannot form new memories after a brain trauma/ death o Like the movie “50 first dates” Animal Models **An Animal model of human amnesia can be created through the induction of medial temporal lesions and measuring resultant changes in memory using the: A. Delayed non-matching Sample Task - recognition over time Example: A monkey is given an object to rememberthen a blind fold is placed on the monkey for a length of time= delay meanwhile a different object is placed in front of the monkey, after the blindfold is removed the monkey must identify the different object - This task teaches the monkey to remove the object that does not look like the object they were just looking at previously o Small delay = Seconds – 10 mins o Long delay= 30 min – hours requires it to use its long term memory A normal monkey will more or less remember up to 10 min after In a monkey with a lesioned medial temporal lobe, it will more likely make a mistake as time goes on B. Morris water maze – understanding spatial memory Somewhere in a tub of water there is a little platform right under the surface of the water - Then a rat is placed in the tub, the only way to escape is to get on top of the platform o The faster the rat finds the platform after 10 trials = learning - Rats with hippocampal lesions fail to learn the location of the submerged platform, swimming in a random fashion until they arrive at the platform even after 10 or infinite trials. Place Cells: Specialized cells in rat hippocampus that encode specific spatial locations in the environment Human Models ** There is evidence of hippocampal involvement in human spatial learning and memory as well A. Maguire’s study of London Taxi drivers - He found that those who used their hippocampus more had larger hippocampal volume AKA hippocampal growth - Those who were taxi drivers longer had greater volume/growth in the hippocampus B. Maguire’s PET study -Used a navigation task for subjects under a PET scan had to find their way through a virtual world - Findings revealed significant hippocampal activations Implicit Memory Long-term memory of tasks, skills, and procedures that occurs outside of conscious awareness H.M. cannot form new long-term declarative memories but can form new long-term implicit memories Basal Ganglia: Caudate and the Putamen (striatum) play an important role in the formation of implicit memory o Dopaminergic inputs to the striatum are critical for normal function. Parkinson’s patients show significant deficits in implicit memory tasks du to this lack. Rain prediction task (subconscious learning) - Amnesia subjects (damaged MTL, intact Basal Ganglia) learned at a lower rate than the control but had a steady improvement with more trials - Parkinsons subjects (Intact MTL, damaged basal ganglia) had no improvement in correct responses after 50 trials Example Question: A given neurons in M1 will control a single muscle of the body Answer: False. A population of M1 neurons signal a set in the spinal cord Example Question: Damage to the rubrospinal tract in the human will lead to paralysis Answer: False Example Question: Which of the following has the largest representation within primary motor cortex. A. Foot B. Stomach C. Hand D. Arm Answer: C. Hand. Hand and face are the most represented in the M1 since they require the significant amounts of fine motor control Example Question: Suppose you are recording from the arm representation of macaque M1 as the monkey performs a motor task moving joystick toward one of five targets (right). Out of the cells from which you are recording, six exhibit significantly increased firing rates and are tuned to preferred direction of 70, 40, 180, 150, 40, and 60 degrees. Which direction will the monkey move its arm? Answer: 90 degrees (take the average of the numbers) Example Question: Which of the following best summarizes the result of LTP A. Smaller EPSPs B. Larger EPSPs C. Smaller action potentials D. Larger action Potentials Answer: B. Larger EPSPs Example Question: The ____ receptor is most critical for the induction of LTP A. AMPA B. NMDA C. Kinase D. Kainate Answer: NMDA Example Question: What do you suppose will happen if we perform an eye blink conditioning procedure after administering a large dose of APV? Answer: You would NOT get this effect because APV blocks NMDA receptors and causes you to lose the ability for LTP learning AKA it prevents your neurons from learning so therefore they begin forgetting.
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