Chapter 9 Learning, Memory, and Amnesia How Your Brain Stores Information <ul><li>This multimedia product and its contents...
The Brain Changes its Functioning in Response to Experience <ul><li>Learning –how experience changes the brain </li></ul><...
Effects of Bilateral Medial Temporal Lobectomy <ul><li>H.M. – an epileptic who had his temporal lobes removed in 1953 </li...
Amnesia <ul><li>Retrograde (backward-acting) – unable to remember the past </li></ul><ul><li>Anterograde (forward-acting) ...
Assessing H.M. <ul><li>Digit span – H.M. can repeat digits as long as the time between learning and recall is within the l...
Assessing H.M. <ul><li>H.M. readily “learns” responses through Pavlovian (classical) conditioning </li></ul><ul><li>H.M. c...
Scientific Contributions of H.M.’s Case <ul><li>Medial temporal lobes are involved in memory </li></ul><ul><li>Short-term ...
Scientific Contributions of H.M.’s Case <ul><li>Memory may exist but not be recalled – as when H.M. exhibits a skill he do...
Explicit Vs Implicit Memories <ul><li>Explicit memories – conscious memories </li></ul><ul><li>Implicit memories – unconsc...
Medial Temporal Lobe Amnesia <ul><li>Not all with this form of amnesia are unable form new explicit long-term memories – a...
Effects of Cerebral Ischemia on the Hippocampus and Memory <ul><li>R.B. suffered damage to just one part of the hippocampu...
Korsakoff’s Syndrome <ul><li>Most commonly seen in who? </li></ul><ul><li>Alcoholics </li></ul><ul><li>Also seen in indivi...
Korsakoff’s Syndrome <ul><li>Characterized by amnesia, confusion, personality changes, and physical problems </li></ul><ul...
Korsakoff’s Syndrome <ul><li>Amnesia comparable to medial temporal lobe amnesia in the early stages </li></ul><ul><ul><li>...
What damage causes the amnesia seen in Korsakoff’s? <ul><li>Hypothalamic mammillary bodies? </li></ul><ul><ul><li>No – Kor...
Alzheimer’s Disease (AD) <ul><li>Begins with slight loss of memory and progresses to dementia </li></ul><ul><li>General de...
What damage causes the amnesia seen in AD? <ul><li>Decreased acetylcholine </li></ul><ul><ul><li>Due to basal forebrain de...
Posttraumatic Amnesia <ul><li>Concussions may cause retrograde amnesia for the period before the blow and some anterograde...
Gradients of Retrograde  Amnesia and Memory Consolidation <ul><li>Concussions disrupt consolidation (storage) of recent me...
The Hippocampus and Consolidation <ul><li>What role does the hippocampus play in consolidation? </li></ul><ul><li>Some hav...
Object-Recognition Memory <ul><li>Early animal models of amnesia involved implicit memory and assumed the hippocampus was ...
Testing object-recognition memory
Delayed Nonmatching-to-Sample Test for Rats <ul><li>Aspiration used to lesion the hippocampus in monkeys – resulting in ad...
Object-Recognition Deficits and  Medial Temporal Lobectomy <ul><li>Neuroanatomical basis of resulting deficits? </li></ul>...
A Paradox <ul><li>Removing the hippocampus has a moderate effect on object recognition while ischemia-induced lesions to a...
A Hypothesis <ul><li>Ischemia-induced hyperactivity of CA1 pyramidal cells damages neurons outside of the hippocampus </li...
A Hypothesis <ul><li>Ischemia-induced hyperactivity leads to extrahippocampal damage that explains ischemia-induced object...
The Hippocampus <ul><li>Rhinal cortex plays an important role in object recognition </li></ul><ul><li>Hippocampus plays a ...
 
Comparative Studies of the Hippocampus <ul><li>Hippocampus seems to play a role in spatial memory in many species – not ju...
Theories of Hippocampal Function <ul><li>Cognitive map theory – constructs and stores allocentric maps of the world </li><...
Where Are Memories Stored? <ul><li>Each memory is stored diffusely throughout the brain structures that were involved in i...
Where are memories stored? <ul><li>Inferotemporal cortex – visual perception of objects – changes in activity seen with vi...
Where are memories stored? <ul><li>Prefrontal cortex – damage leads to problems with tasks involving a series of responses...
Where are memories stored? <ul><li>Cerebellum and striatum – sensorimotor tasks </li></ul><ul><li>Cerebellum – stores memo...
Synaptic Mechanisms of Learning and Memory <ul><li>What is happening within the brain structures involved in memory? </li>...
LTP as a Neural Mechanism of Learning and Memory <ul><li>Consistent with the synaptic changes hypothesized by Hebb </li></...
LTP as a Neural Mechanism of Learning and Memory <ul><li>Elicited by levels of stimulation that mimic normal neural activi...
LTP as a Neural Mechanism of Learning and Memory <ul><li>Much indirect evidence supports a role for LTP in learning and me...
Induction of LTP: Learning <ul><li>Usually studied where NMDA glutamate receptors are prominent </li></ul><ul><li>NMDA rec...
Induction of LTP: Learning <ul><li>Calcium influx only occurs if there is the co-occurrence that is needed for LTP, leadin...
Maintenance and Expression of LTP: Storage and Recall <ul><li>Pre- and postsynaptic changes </li></ul><ul><li>LTP is only ...
Maintenance and Expression of LTP: Storage and Recall <ul><li>How are presynaptic and postsynaptic changes coordinated? </...
LTP – A Final Note <ul><li>Most LTP research has focused on NMDA-receptor-mediated LTP in the hippocampus, but LTP is medi...
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Pinel basics ch09

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Pinel basics ch09

  1. 1. Chapter 9 Learning, Memory, and Amnesia How Your Brain Stores Information <ul><li>This multimedia product and its contents are protected under copyright law. The following are prohibited by law: </li></ul><ul><li>any public performance or display, including transmission of any image over a network; </li></ul><ul><li>preparation of any derivative work, including the extraction, in whole or in part, of any images; </li></ul><ul><li>any rental, lease, or lending of the program. </li></ul>
  2. 2. The Brain Changes its Functioning in Response to Experience <ul><li>Learning –how experience changes the brain </li></ul><ul><li>Memory –how changes are stored and subsequently reactivated </li></ul><ul><li>What brain structures are involved in processes of learning and memory? </li></ul>
  3. 3. Effects of Bilateral Medial Temporal Lobectomy <ul><li>H.M. – an epileptic who had his temporal lobes removed in 1953 </li></ul><ul><li>His seizures were dramatically reduced – but so was his memory </li></ul><ul><li>Mild retrograde amnesia and severe anterograde amnesia </li></ul>
  4. 4. Amnesia <ul><li>Retrograde (backward-acting) – unable to remember the past </li></ul><ul><li>Anterograde (forward-acting) – unable to form new memories </li></ul><ul><li>While H.M. is unable to form most types of new long-term memories, his STM is intact </li></ul>
  5. 5. Assessing H.M. <ul><li>Digit span – H.M. can repeat digits as long as the time between learning and recall is within the limits of short-term storage </li></ul><ul><li>Mirror-drawing task – H.M. exhibits improvement with practice. He is able to show skill memory – demonstrating that he can learn some things (also rotary-pursuit and a drawing task) – although he is not aware of it </li></ul>
  6. 6. Assessing H.M. <ul><li>H.M. readily “learns” responses through Pavlovian (classical) conditioning </li></ul><ul><li>H.M. can learn some things, but has no memory of having learned them </li></ul>
  7. 7. Scientific Contributions of H.M.’s Case <ul><li>Medial temporal lobes are involved in memory </li></ul><ul><li>Short-term memory (STM) and long-term memory (LTM) are distinctly separate </li></ul><ul><li>H.M. is unable to move memories from STM to LTM, a problem with memory consolidation </li></ul>
  8. 8. Scientific Contributions of H.M.’s Case <ul><li>Memory may exist but not be recalled – as when H.M. exhibits a skill he does not know he has learned </li></ul><ul><li>H.M. forms new implicit memories, but not new explicit memories </li></ul>
  9. 9. Explicit Vs Implicit Memories <ul><li>Explicit memories – conscious memories </li></ul><ul><li>Implicit memories – unconscious memories, as when H.M. shows the benefits of prior experience </li></ul><ul><li>Repetition priming tests – used to assess implicit memory – performance in identifying word fragments is improved when the words have been seen before </li></ul>
  10. 10. Medial Temporal Lobe Amnesia <ul><li>Not all with this form of amnesia are unable form new explicit long-term memories – as was the case with H.M. </li></ul><ul><li>Semantic memory (general information) may function normally while episodic memory (events that one has experienced) does not – they are able to learn facts, but do not remember doing so (the episode when it occurred) </li></ul>
  11. 11. Effects of Cerebral Ischemia on the Hippocampus and Memory <ul><li>R.B. suffered damage to just one part of the hippocampus (CA1 pyramidal cell layer) and developed amnesia </li></ul><ul><li>R.B.’s case suggests that hippocampal damage alone can produce amnesia </li></ul><ul><li>H.M.’s damage – and amnesia – was more severe than R.B.’s </li></ul>
  12. 12. Korsakoff’s Syndrome <ul><li>Most commonly seen in who? </li></ul><ul><li>Alcoholics </li></ul><ul><li>Also seen in individuals with a thiamine-deficient diet </li></ul><ul><li>Alcohol causes a disruption in the body’s ability to use thiamine </li></ul>
  13. 13. Korsakoff’s Syndrome <ul><li>Characterized by amnesia, confusion, personality changes, and physical problems </li></ul><ul><li>Typically damage in the medial diencephalon – medial thalamus + medial hypothalamus </li></ul>
  14. 14. Korsakoff’s Syndrome <ul><li>Amnesia comparable to medial temporal lobe amnesia in the early stages </li></ul><ul><ul><li>Anterograde amnesia for episodic memories </li></ul></ul><ul><li>Differs in later stages </li></ul><ul><ul><li>Severe retrograde amnesia develops </li></ul></ul><ul><li>Differs in that it is progressive, complicating its study </li></ul>
  15. 15. What damage causes the amnesia seen in Korsakoff’s? <ul><li>Hypothalamic mammillary bodies? </li></ul><ul><ul><li>No – Korsakoff’s amnesia is seen in cases without such damage </li></ul></ul><ul><li>Thalamic mediodorsal nuclei? </li></ul><ul><ul><li>Possibly – damage is seen here when there is no mammillary damage </li></ul></ul><ul><li>Cause is not likely to be damage to a single diencephalic structure </li></ul>
  16. 16. Alzheimer’s Disease (AD) <ul><li>Begins with slight loss of memory and progresses to dementia </li></ul><ul><li>General deficits in predementia AD </li></ul><ul><ul><li>Major anterograde and retrograde amnesia in explicit memory tests </li></ul></ul><ul><ul><li>Deficits in STM and some types of implicit memory – verbal and perceptual </li></ul></ul><ul><li>Implicit sensorimotor memory is intact </li></ul>
  17. 17. What damage causes the amnesia seen in AD? <ul><li>Decreased acetylcholine </li></ul><ul><ul><li>Due to basal forebrain degeneration </li></ul></ul><ul><ul><li>Basal forebrain strokes can cause amnesia and attention deficits which may be mistaken for memory deficits </li></ul></ul><ul><li>Medial temporal lobe and prefrontal cortex also involved </li></ul><ul><li>Damage is diffuse – resulting amnesia is likely a consequence of acetylcholine depletion and brain damage </li></ul>
  18. 18. Posttraumatic Amnesia <ul><li>Concussions may cause retrograde amnesia for the period before the blow and some anterograde amnesia after </li></ul><ul><li>The same is seen with comas, with the severity of the amnesia correlated with the duration of the coma </li></ul><ul><li>Period of anterograde amnesia suggests a temporary failure of memory consolidation </li></ul>
  19. 19. Gradients of Retrograde Amnesia and Memory Consolidation <ul><li>Concussions disrupt consolidation (storage) of recent memories </li></ul><ul><li>Hebb – memories are stored in the short term by neural activity </li></ul><ul><li>Interference with this activity prevents memory consolidation </li></ul><ul><ul><li>Blows to the head (i.e., concussion) </li></ul></ul><ul><ul><li>ECS (electroconvulsive shock) </li></ul></ul>
  20. 20. The Hippocampus and Consolidation <ul><li>What role does the hippocampus play in consolidation? </li></ul><ul><li>Some have proposed that memory storage structures store memories for as long as they exist and eventually an engram forms </li></ul><ul><li>Engram – a change in the brain that stores a memory </li></ul>
  21. 21. Object-Recognition Memory <ul><li>Early animal models of amnesia involved implicit memory and assumed the hippocampus was key </li></ul><ul><li>1970’s – monkeys with bilateral medial temporal lobectomies show LTM deficits in the delayed nonmatching-to-sample test </li></ul><ul><li>Like H.M., performance was normal when memory needed to be held for only a few seconds (within the duration of STM) </li></ul>
  22. 22. Testing object-recognition memory
  23. 23. Delayed Nonmatching-to-Sample Test for Rats <ul><li>Aspiration used to lesion the hippocampus in monkeys – resulting in additional cortical damage </li></ul><ul><li>Extraneous damage is limited in rats due to lesion methods used </li></ul><ul><li>Bilateral damage to rat hippocampus, amygdala, and rhinal cortex produces the same deficits seen in monkeys with hippocampal lesions </li></ul>
  24. 24. Object-Recognition Deficits and Medial Temporal Lobectomy <ul><li>Neuroanatomical basis of resulting deficits? </li></ul><ul><li>Bilateral removal of the rhinal cortex > object-recognition deficits </li></ul><ul><li>Bilateral removal of the hippocampus > no or moderate effects on object recognition </li></ul><ul><li>Bilateral removal of the amygdala? </li></ul><ul><ul><li>No effect on object-recognition. </li></ul></ul>
  25. 25. A Paradox <ul><li>Removing the hippocampus has a moderate effect on object recognition while ischemia-induced lesions to a small part of it leads to severe deficits </li></ul><ul><li>How can this be? </li></ul>
  26. 26. A Hypothesis <ul><li>Ischemia-induced hyperactivity of CA1 pyramidal cells damages neurons outside of the hippocampus </li></ul><ul><li>Extrahippocampal damage not readily detectable </li></ul><ul><li>Extrahippocampal damage is largely responsible for ischemia-induced object recognition deficits. </li></ul><ul><li>Evidence? </li></ul>
  27. 27. A Hypothesis <ul><li>Ischemia-induced hyperactivity leads to extrahippocampal damage that explains ischemia-induced object recognition deficits </li></ul><ul><ul><li>Bilateral hippocampectomy prevents ischemia-induced deficits </li></ul></ul><ul><ul><li>Supported by functional brain-imaging studies </li></ul></ul>
  28. 28. The Hippocampus <ul><li>Rhinal cortex plays an important role in object recognition </li></ul><ul><li>Hippocampus plays a key role in memory for spatial location </li></ul><ul><ul><li>Hippocampal lesions producesdeficits on Morris water and radial arm mazes </li></ul></ul><ul><ul><li>Many hippocampal cells are place cells – responding when a subject is in a particular place </li></ul></ul>
  29. 30. Comparative Studies of the Hippocampus <ul><li>Hippocampus seems to play a role in spatial memory in many species – not just rats </li></ul><ul><li>Food-caching birds - caching and retrieving is needed for hippocampal growth </li></ul><ul><li>Primate studies are inconsistent – no place cells </li></ul><ul><li>Differences may be due to differences in testing paradigms </li></ul><ul><ul><li>Navigating through the environment Vs location on a computer screen </li></ul></ul>
  30. 31. Theories of Hippocampal Function <ul><li>Cognitive map theory – constructs and stores allocentric maps of the world </li></ul><ul><li>Configural association theory – involved in retaining the behavioral significance of combinations of stimuli </li></ul><ul><li>Involved in recognizing spatial arrangements of objects </li></ul>
  31. 32. Where Are Memories Stored? <ul><li>Each memory is stored diffusely throughout the brain structures that were involved in its formation. </li></ul><ul><li>Hippocampus – spatial location </li></ul><ul><li>Rhinal cortex – object recognition </li></ul><ul><li>Mediodorsal nucleus – Korsakoff’s </li></ul><ul><li>Basal forebrain – Alzheimer’s disease </li></ul><ul><li>Damage to a variety of structures results in memory deficits. </li></ul>
  32. 33. Where are memories stored? <ul><li>Inferotemporal cortex – visual perception of objects – changes in activity seen with visual recall </li></ul><ul><li>Amygdala – emotional learning – lesion leads to lack of learned fear </li></ul><ul><li>Prefrontal cortex – temporal order of events and working memory </li></ul>
  33. 34. Where are memories stored? <ul><li>Prefrontal cortex – damage leads to problems with tasks involving a series of responses </li></ul><ul><li>Different part of this structure may mediate different types of working memory – some evidence from functional brain imaging studies </li></ul>
  34. 35. Where are memories stored? <ul><li>Cerebellum and striatum – sensorimotor tasks </li></ul><ul><li>Cerebellum – stores memories of sensorimotor skills – conditioned eyeblink, for example </li></ul><ul><li>Striatum – habit formation – associations between stimuli and responses </li></ul>
  35. 36. Synaptic Mechanisms of Learning and Memory <ul><li>What is happening within the brain structures involved in memory? </li></ul><ul><li>Hebb – changes in synaptic efficiency are the basis of long-term memory </li></ul><ul><li>Long-term potentiation (LTP) – synapses are effectively made stronger by repeated stimulation </li></ul>
  36. 37. LTP as a Neural Mechanism of Learning and Memory <ul><li>Consistent with the synaptic changes hypothesized by Hebb </li></ul><ul><ul><li>LTP can last for many weeks. </li></ul></ul><ul><ul><li>LTP only occurs if presynaptic firing is followed by postsynaptic firing </li></ul></ul><ul><li>Hebb’s postulate for learning </li></ul><ul><ul><li>Co-occurrence is necessary for learning and memory </li></ul></ul>
  37. 38. LTP as a Neural Mechanism of Learning and Memory <ul><li>Elicited by levels of stimulation that mimic normal neural activity </li></ul><ul><li>LTP effects greatest in brain areas involved in learning and memory </li></ul><ul><li>Learning can produce LTP-like changes </li></ul><ul><li>Drugs that impact learning often have parallel effects on LTP </li></ul>
  38. 39. LTP as a Neural Mechanism of Learning and Memory <ul><li>Much indirect evidence supports a role for LTP in learning and memory </li></ul><ul><li>LTP can be viewed as a three-part process: </li></ul><ul><ul><li>Induction (learning) </li></ul></ul><ul><ul><li>Maintenance (memory) </li></ul></ul><ul><ul><li>Expression (recall) </li></ul></ul>
  39. 40. Induction of LTP: Learning <ul><li>Usually studied where NMDA glutamate receptors are prominent </li></ul><ul><li>NMDA receptors do not respond maximally unless glutamate binds and the neuron is already depolarized </li></ul><ul><li>Calcium channels do not open fully unless both conditions are met </li></ul>
  40. 41. Induction of LTP: Learning <ul><li>Calcium influx only occurs if there is the co-occurrence that is needed for LTP, leading to the binding of glutamate at an NMDA receptor that is already depolarized </li></ul><ul><li>Calcium influx may activate protein kinases that induces changes causing LTP </li></ul>
  41. 42. Maintenance and Expression of LTP: Storage and Recall <ul><li>Pre- and postsynaptic changes </li></ul><ul><li>LTP is only seen in synapses where it was induced </li></ul><ul><li>Protein-synthesis underlies long-term changes </li></ul><ul><li>Long-lasting changes in extracellular glutamate levels </li></ul>
  42. 43. Maintenance and Expression of LTP: Storage and Recall <ul><li>How are presynaptic and postsynaptic changes coordinated? </li></ul><ul><li>Nitric oxide synthesized in postsynaptic neurons in response to calcium influx may diffuse back to presynaptic neurons </li></ul><ul><li>Structural changes are now a well-established consequence of LTP </li></ul>
  43. 44. LTP – A Final Note <ul><li>Most LTP research has focused on NMDA-receptor-mediated LTP in the hippocampus, but LTP is mediated by different mechanisms elsewhere. </li></ul><ul><li>LTD, long-term depression, also exists </li></ul><ul><li>Why should there be a variety of mechanisms and places that underlie learning and memory? </li></ul>

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