Introduction to Physiological Psychology Learning and Memory II

Transcription

1 Introduction to Physiological Psychology Learning and Memory II cogsci.ucsd.edu/~ksweeney/psy260.html Memory Working Memory Long-term Memory Declarative Memory Procedural Memory Episodic Memory Semantic Memory 1

2 What can possibly go wrong? n Anterograde Amnesia: Amnesia for events occurring after the precipitating event. n Retrograde Amnesia: Amnesia for events occurring before the precipitating event. Hippocampus 3D 2

3 H.M. Effects of Bilateral Medial Temporal Lobectomy n Minor seizure beginning at age 10, major seizures beginning age 16 n Severe, persistent seizure condition- not controlled with anticonvulsants n By mid-20 s, condition was so severe he was unable to work n Surgery at age 27: Bilateral medial temporal lobe resection. Tissues typically excised in medial temporal lobectomy 3

4 n In HM, the amygdala, entorhinal and perirhinal cortices, and about twothirds of the hippocampus were removed 4

5 H.M. Effects of Bilateral Medial Temporal Lobectomy n Seizures were dramatically reduced but so was his long-term memory! n Evaluation two years post-surgery (April, 1955) Gave date as March 1953, and age as 27 Talked to physician before entering exam room, but at exam had no recollection of him Memories of his past were clear No deficits in perception, abstract thought, reasoning As he progressed through tests, retained no memory of earlier tests, and didn t recognize them when presented a second time. What s wrong with H.M., and what does it tell us about functions of Hippocampus and MTL? n What CAN he do? Intellect is normal Can remember the past (pre-surgery) He has relatively little retrograde amnesia His long-term memory is intact Can carry on excellent, short conversation His working memory is intact Can learn new skills at a normal rate- and retains those skills over long periods of time His procedural memory is intact 5

6 n Procedural memory is intact! Rotary Pursuit task Mirror Drawing task Other spared learning n Broken drawing recognition n Preference task melodies Valenced faces n Repetition priming n Serial reaction time task 6

7 What s wrong with H.M., and what does it tell us about functions of Hippocampus and MTL? n What CAN T he do? Doesn t retain new semantic or episodic information Can t form new declarative memories. The Medial Temporal Lobe: Crucial in the Declarative Memory System n Damage to these areas usually results in anterograde amnesia: patients are unable to form new declarative memories. n Can also result in retrograde amnesia: typically graded. n Non-declarative memory is not affected. 7

8 What does H.M. tell us about role of Hippocampus and MTL? n Hippocampus is essential for the formation, but not the storage or retrieval, of long-term declarative memory n Memory depends on Hippocampus for a short duration n Hippocampus does not mediate short-term memory What does H.M. tell us about role of Hippocampus and MTL? n STM and LTM are distinctly separate H.M. is unable to move memories from STM to LTM, a problem with memory consolidation n Memory may exist but not be recalled as when H.M. exhibits a skill he does not know he has learned 8

9 Explicit vs. Implicit Memories n Explicit memories conscious memories n Implicit memories unconscious memories, as when H.M. shows the benefits of prior experience Repetition priming tests- word fragments Incomplete pictures test- picture fragments Also, new songs, response to stranger Medial Temporal Lobe Amnesia n Often (but not always) unable to form new explicit long-term memories n Semantic memory (general information) may function normally while episodic memory (events that one has experienced) does not able to learn facts, but do not remember doing so (the episode when it occurred) n Medial temporal lobe amnesiacs may have trouble imagining future events 9

10 Spared Leaning Abilities n Perceptual Learning: Intact n Stimulus-Response Learning: Intact n Motor Learning: Intact n But Relational Learning Hippocampus 3D 10

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12 Information pathway in hippocampal formation n Entorhinal cortex > n Dentate gyrus > n CA3 > n CA1 & forebrain Long Term Potentiation n Deliver single pulse to perforant path n Measure population EPSP in dentate gyrus n Stimulate perforant path with series of rapid pulses n After rapid stimulation response in dentate gyrus to a single pulse is increased- LTP has occurred!! 12

13 Associative LTP n Exactly as Hebb had suspected: when both a weak and a strong synapse are stimulated at ~the same time, the weak synapse becomes strengthened. n Neurons that fire together, wire together 13

14 Remember Temporal Summation? n The reason many pulses are necessary is because for LTP to occur, the postsynaptic cell must already be depolarized. n Why? Temporal summation NMDA and AMPA n Among the glutamate receptors: NMDA and AMPA n Glutamate binds to NMDA receptors, which controls a calcium (Ca2+) channel. n So, Ca2+ rushes in, right? NO! 14

15 NMDA and AMPA n At rest, that same calcium channel is guarded by a magnesium ion (Mg2+), so calcium can t get in through NMDA receptors. n That Mg2+ ion won t budge unless cell is depolarized. n But cell can t depolarize unless Ca2+ can get in, right? NO! NMDA and AMPA n If a weak synapse is active by itself, nothing happens n BUT- if the cell has just fired due to a strong synapse elsewhere else on the cell, a dendritic spike will depolarize the membrane 15

16 NMDA and AMPA n Depolarization kicks the Mg2+ ion out, and NOW Ca2+ ions can enter the cell. n and an association between those two synapses is formed. We still don t have LTP! n Ca2+ ions entering the cell bind with the enzyme CaM- KII n CaM-KII causes more AMPA receptors to to move to post-synaptic membrane. n More AMPA receptors means it s easier to depolarize the cell in the future. 16

17 We still don t have LTP! n Ca2+ ions entering the cell bind with the enzyme CaM- KII n CaM-KII causes more AMPA receptors to to move to post-synaptic membrane. n More AMPA receptors means it s easier to depolarize the cell in the future. n For Ca2+ to enter the cell, NMDA receptors have to be activated by glutamate AND subjected to depolarization simultaneously. n The fact that both these things must occur together means that NMDA receptors are coincidence detectors. n Thus, they are crucial for LTP. 17

18 Perceptual Learning n Learning enables us to adapt to our environment and to respond to changes in it: In particular, learning provides us with the ability to perform an appropriate behavior in an appropriate situation. n The first part of learning involves learning to perceive particular stimuli: Perceptual learning involves learning to recognize things, not what to do when they are present. n Perceptual learning can involve learning to recognize entirely new stimuli, or it can involve learning to recognize changes or variations in familiar stimuli. 18

19 Perceptual Learning n Visual information: After the first level of analysis the information is sent to the extrastriate cortex, which surrounds the primary visual cortex (striate cortex, V1). n After analyzing particular attributes of the visual scene, such as form, color, and movement, subregions of the extrastriate cortex send the results of their analysis to the next level of the visual association cortex, which is divided into two streams. Perceptual Learning n The ventral stream involved with object recognition, continues ventrally into the inferior temporal cortex. n The dorsal stream involved with perception of the location of objects, continues dorsally into the posterior parietal cortex. n The ventral stream is involved with the what of visual perception; the dorsal stream is involved with the where. 19

20 PET study of where/what dichotomy Perceptual Learning n Specific kinds of visual information can activate very specific regions of visual association cortex. n The investigators presented subjects with photographs that implied motion for example, an athlete getting ready to throw a ball. n They found that photographs like these, but not photographs of people remaining still, activated area MT/MST. 20

21 Stimulus-Response Learning (Classical Conditioning) Extinction Several trials of the tone-alone (with no shock given). Intact rats show normal blood pressure and movement to the tone, following this (extinction) training. 21

22 The Amygdala n n n The amygdala (almond) sits at the tip of the hippocampus It receives information from virtually the entire brainafter different amounts of processing It projects to many areas, but one of the strongest projections is to the entorhinal cortex! The Amygdala n As a rat learns the pairing, (more) neurons become more responsive. But after several tones without the pairing, firing rates return to baseline. If rendered inactive, conditioning does not occur! Firing in the lateral amygdala 22

23 Basic Fear Circuitry Creation and Extinction of Fear Memories n The lateral nucleus of the amygdala receives information from somatosensory system and auditory system. n It projects (directly and indirectly) to central nucleus, which mediates expression of fear response 23

24 Creation and Extinction of Fear Memories n With a lesion to the lateral nucleus, a rat will not learn the conditioned emotional response. n With a lesion to the central nucleus, the conditioned response is reduced. Stimulus-Response Learning: Instrumental Conditioning n Instrumental conditioning is the means by which we profit from experience If the response is already known, we need strengthening of connections b/t neural circuits that detect relevant stimuli, and those that control the relative response If a new response is needed, then motor learning will take place 24

25 Instrumental Conditioning n Circuits responsible for instrumental conditioning begin in sensory association cortices and end in motor association cortex. Instrumental Conditioning n Two major pathways from sensory to motor association areas: Direct transcortical connections- involved in STM, acquisition of episodic memories and of complex behaviors that involve deliberation or instruction (slow and laborious) Connections via the basal ganglia and thalamus- which are involved as behaviors become automatic and routine (fast and easy) 25

26 Basal Ganglia n Neostriatum (caudate and putamen) receives sensory info from all areas of cortex n Projects to globus pallidus, which projects to premotor and supplementary motor circuits (involved in planning and execution of movements), and to primary motor cortex Basal Ganglia n Damage to neostriatum makes it difficult to learn to make a visually guided response n but does NOT disrupt visual perceptual learning. 26

27 Instrumental Conditioning n As we deliberately perform a complex behavior, the basal ganglia receive information both about the stimuli that are present and the responses we are making. n At first the basal ganglia are passive observers of the situation, but as the behaviors are repeated again and again, the basal ganglia begin to learn what to do. n Eventually, they take over most of the details of the process, leaving the transcortical circuits free to do something else- We need no longer think about what we are doing. Relational Learning 27

28 n Spatial Memory Relational Learning n Spatial information need not be declared (we can demonstrate our topographical memories by successfully getting from place to place) n BUT: people with anterograde amnesia are often unable to consolidate information about the location of rooms, corridors, buildings, roads, and other important items in their environment. n Spatial Memory Relational Learning n Bilateral medial temporal lobe lesions produce the most profound impairment in spatial memory, but significant deficits can be produced by damage that is limited to the right hemisphere. n Functional imaging studies have shown that the right hippocampal formation becomes active when a person is remembering or performing a navigational task. 28

29 Relational Learning n Relational Learning in Laboratory Animals n The discovery that hippocampal lesions produced anterograde amnesia in humans stimulated interest in the exact role that this structure plays in the learning process. n Researchers have developed tasks that require relational learning, and on such tasks laboratory animals with hippocampal lesions show memory deficits, just as humans do. Relational Learning n Relational Learning in Laboratory Animals n The Morris water maze requires relational learning; to navigate around the maze, the animals get their bearings from the relative locations of stimuli located outside the maze furniture, windows, doors, and so on, but the maze can be used for nonrelational, stimulus response learning too. 29

30 Relational Learning n Relational Learning in Laboratory Animals n If rats with hippocampal lesions are always released from the same place, they learn this nonrelational, stimulus response task about as well as normal rats do. n However, if they are released from a new position on each trial, they swim in what appears to be an aimless fashion until they finally encounter the platform. 30

31 Relational Learning n Relational Learning in Laboratory Animals n Place cells have receptive fields in the environment. n Place cells are active when the animal is in a particular location in the environment; most typically found in the hippocampal formationbut also in entorhinal cortex. n Evidence indicates that firing of hippocampal place cells appears to reflect the location where an animal thinks it is. 31

32 Hippocampus and spatial memory Hippocampus seems to play role in spatial memory in many species not just rats! n Food-caching birds caching and retrieving is needed for hippocampal growth n Primate studies are inconsistent But perhaps due to poor design! n Taxi drivers! The Hippocampus and Memory for Spatial Location n So Rhinal cortex plays an important role in object recognition n Hippocampus plays a key role in memory for spatial location Hippocampectomy produces deficits on Morris maze and radial arm maze Place cells also found in entorhinal cortex 32