Neuropsychology of Memory

1. Neuropsychology of Memory • Types of memory problems • a pure amnesia is relatively rare • memory problems commonly occur after a traumatic brain injury (TBI) • TBI results in brain damage of two sorts: • lesions • twisting and shearing of brain structures and damage from bony protuberances of brain, particularly of the temporal lobes

2. Neuropsychology of Memory • Memory problems following TBI • post-traumatic amnesia • retrograde amnesia • anterograde amnesia

3. Neuropsychology of Memory • Memory problems following TBI • post-traumatic amnesia • after severe TBI, individuals typically lose consciousness • after they begin to regain consciousness, there is often a gradual recovery during which patients have difficulty keeping tracking of and remembering ongoing events, though there may be islands of lucidity and memory

4. Neuropsychology of Memory • Memory problems following TBI • retrograde amnesia • refers to difficulty remembering events that occurred prior to injury • the duration of amnesia varies but can extend back for several years • duration of retrograde amnesia typically shrinks as time passes

5. Neuropsychology of Memory • retrograde amnesia • duration of retrograde amnesia typically shrinks as time passes • e.g., Russell (1959) described case of TBI as a result of a motorcycle accident • 1 week post accident patient had lost 11 years of memory extending back from injury • 2 weeks post accident patient had lost 2 years of memory • about 10 weeks post injury memories of the last two years gradually returned

6. Neuropsychology of Memory • Memory problems following TBI • retrograde amnesia • formal testing of amnesics using famous faces/famous events has shown that there appears to be recall and recognition for old faces/events

7. Neuropsychology of Memory • retrograde amnesia • Butters & Cermak (1986) reported a case study of an eminent scientist (born 1914) who had written his autobiography only two years prior to becoming amnesic • tested him by asking him questions all drawn from his autobiography

8. Neuropsychology of Memory

9. Neuropsychology of Memory • retrograde amnesia • the pattern of results in some individuals appear to depend upon the nature of the retrieval cue presented • Warrington and McCarthy (1988) showed that an amnesic patient was impaired when shown faces of famous people and asked to recall them • however, performance was normal when tested using recognition procedures

10. Neuropsychology of Memory • Memory problems following TBI • retrograde amnesia • this pattern of results suggests that retrograde amnesia is a retrieval problem • the pattern of damage/recovery -- from most distant to most recent -- has been argued by some to reflect a failure of consolidation (Ribot’s Law)

11. Neuropsychology of Memory • retrograde amnesia (RA) • pattern of memory gradient varies across patients (See Moscovitch et al. 2006) • If lesion restricted to hippocampus, RA extends back a few years only • When lesion includes entire hippocampal formation or extends to adjacent regions, severe ungraded RA (ungraded means that memory loss is equivalent at all time periods since acquisition); some labs have reported graded retroactive amnesia (recent memories are poorer than more remote memories)

12. Neuropsychology of Memory • Memory problems following TBI • anterograde amnesia • refers to problems of learning new facts • although sometimes amnesia is specific to learning of verbal material (following LHD) or visuo-spatial material (following RHD) amnesia usually affects learning of many types of new information

13. Neuropsychology of Memory • Amnesic syndrome • dense form of memory deficit (as assessed by standardized testing) • relatively spared performance in other domains

14. Neuropsychology of Memory • Causes of amnesia • Korsakoff’s syndrome: drinking too much, eating too little, resulting in a thiamine deficiency and brain damage • damage to brain following viral infection (e.g., viral encephalitis) • lesion to critical brain regions -- e.g., HM • anoxia following heart attack, suicide attempt, etc.

15. Neuropsychology of Memory • Korsakoff’s syndrome • History • 1881, a neurologist Carl Wernicke described a syndrome involving ataxia, oculomotor problems (gaze palsies and nystagmus), peripheral neuropathy, and confusion. This condition came to be known as Wernicke's encephalopathy • Korsakoff identified several patients with confusion, confabulation, sensory loss (especially of the feet), and anterograde amnesia

16. Neuropsychology of Memory • Korsakoff’s syndrome • Terminology • Ataxia– problems of muscular coordination; e.g., people ‘duck walk’, feet apart, stiff-legged • oculomotor problems (gaze palsies and nystagmus); abnormal eye movements—palsy = paralysis; nystagmus = involuntary rapid eye movements • peripheral neuropathy = functional disturbance of peripheral nervous system

17. Neuropsychology of Memory • Korsakoff’s syndrome • History • 1901 Bonhoffer realized Korsakoff’s patients had passed through the Wernicke's encephalopathy stage • today syndrome is called alcoholic Korsakoff syndrome. There are seven primary defining features of this disease:

18. Neuropsychology of Memory • Defining features of alcoholic Korsakoff syndrome • a. a retrograde amnesia with a temporal gradient (i.e., better preserved memories from the remote than from the more recent past) • b. anterograde amnesia, meaning a nearly complete inability to learn new information from the time of the disease onset onward.

19. Neuropsychology of Memory • c. confabulation, which is a tendency to "fill in the gaps" of one's memories with plausible made-up stories. • confabulations are rare among chronic Korsakoff patients who've had the disease for more than 5 years. Patients in the chronic stage are more likely to say "I don't know" or remain silent when faced with memory failures rather than to invent stories.

20. Neuropsychology of Memory • d. generally preserved IQ, including a normal digit span. • e. personality changes, the most common of which is apathy, passivity and indifference • inability to formulate and follow through a series of plans • f. lack of insight into their condition.

21. Neuropsychology of Memory • Korsakoff’s syndrome • worst impairments are on episodic memory tests, including list learning of words, figures, or faces, paragraph recall. • relatively preserved semantic memory, including normal verbal fluency, vocabulary, rules of syntax, and basic arithmetic operations • intact sensori-motor memory (mirror tracing, mirror reading, pursuit rotor) • intact performance on implicit memory tests

22. Neuropsychology of Memory • Neuropathology of Korsakoff’s syndrome • most sources attribute the amnesia to combined lesions in two diencephalic structures: regions of the thalamus and the mammillary bodies of the hypothalamus

23. Neuropsychology of Memory • HM, Hippocampal man • prototype of amnesia attributable to hippocampal damage • bilateral mesial temporal lobe resection extending 8 cm. back from the temporal tips, including the uncus and amygdala, and destroying the anterior two-thirds of the hippocampus and hippocampal gyrus, for the treatment of intractable epilepsy in 1954. • surgery led to a permanent, severe anterograde amnesia, limited retrograde amnesia, and normal intelligence.

24. Neuropsychology of Memory • HM, Hippocampal man • Perceptual, motor, and cognitive functioning • IQ above average; language function intact, speech fluency slightly impaired; spelling poor • Appreciation of puns and linguistic ambiguities • Difficulty with some spatial tasks (e.g., could not use spatial floor plan to navigate through a novel building, but could reproduce a floor plan of family home)

25. Neuropsychology of Memory • HM, Hippocampal man • Memory • Almost no capacity for new learning regardless of materials (short stories, word lists, pictures, etc.) • But there are certain tasks requiring memory that are intact in H.M. • Mirror drawing

26. Neuropsychology of Memory • Multiple memory systems perspective • HM also had a retrograde amnesia; that is, he forgets events that occurred prior to surgery • His retrograde amnesia is temporally graded: The closer the event to surgery the less likely he was able to recall it • This finding suggests that the medial temporal lobes are not always required to retrieve memories

27. Neuropsychology of Memory • Multiple memory systems perspective • In 1962 Milner and colleagues showed that HM improved on tasks requiring skilled movements • HM’s improvement was comparable to controls • Skill was called ‘mirror tracing’ because it requires participants to draw the outline of a star while looking at the reflection of his hand and the star on the mirror • HM had no conscious recollection of having done this task in the past • This is now viewed as a form of non-declarative or implicit memory task

28. H.M.’s skilled learning performance

29. Encoding and Retrieval from long-term memory (LTM) • Multiple memory systems perspective • Other forms of implicit memory include priming effects that were reported by Warrington & Weiskrantz (1968) • In this study amnesics shown list of words (e.g., absent); at test participants were given word stem completion task (e.g., abs_____), and instructed to complete with first word that comes to mind • Results showed that amnesics (and controls) were more likely to complete word stems with previously studied words

30. Neuropsychology of Memory • HM, Hippocampal man • Gollins partial picture task • Task involves recognition of fragmented line drawings of 20 objects • 5 cards for each object with each card showing more and more fragments of the completed drawings • Participants are shown the 20 most difficult cards, then the next-most-difficult cards etc.

31. Neuropsychology of Memory • HM, Hippocampal man • Gollins partial picture task • Task involves recognition of fragmented line drawings of 20 objects • 5 cards for each object with each card showing more and more fragments of the completed drawings as shown in Figure • Participants are shown the 20 most difficult cards, then the next-most-difficult cards etc.

32. Neuropsychology of Memory • HM, Hippocampal man • Gollins partial picture task (Warrington & Weiskrantz, 1968 Nature, 217, 972-974 • HM and normal controls performed this task, and then after an hour of intervening activity performed the task again • Results shown in next figure show that H.M. and controls made fewer errors on immediate tests as figures became more complete and when tested after a 1 hour delay there was memory retention • Conclusion. Perceptual memory is intact in H.M.; perceptual memory does not appear to be mediated by medial temporal structures

34. Neuropsychology of Memory • HM, Hippocampal man • Dot pattern study (Gabrieli, 1990, Neuropsychologia, 28, 417-427) • H.M. and controls were shown a series of 5 dots arranged in a unique pattern • Baseline draw. Participants (Ps) were instructed to draw any pattern they wanted (to control for pre-existing biases) • Experiment. Ps were shown a target pattern & copied that pattern on dots • After 6 hour delay, Ps were shown dots and were instructed to draw on dots any pattern they wanted

35. Neuropsychology of Memory • HM, Hippocampal man • Dot pattern study (Gabrieli, 1990, Neuropsychologia, 28, 417-427) • H.M. and controls were shown a series of 5 dots arranged in a unique pattern • Baseline draw. Participants (Ps) were instructed to draw any pattern they wanted (to control for pre-existing biases) • Experiment. Ps were shown a target pattern & copied that pattern on dots • After 6 hour delay, Ps were shown dots and were instructed to draw on dots any pattern they wanted

36. Neuropsychology of Memory • HM, Hippocampal man • Dot pattern study (Gabrieli, 1990, Neuropsychologia, 28, 417-427) • Implicit memory – percentage of target figures drawn that were identical to the copied target pattern (dots drawn in the baseline condition were not scored) • Explicit memory – Recognition memory – Ps were shown 4 dot patterns that drawn on the dots and selected the dot pattern that had been copied

37. Dot pattern • Top figure shows dot pattern and target stimuli • Left panel of bottom figure shows explicit performance and right panel shows implicit performance of H.M. and Controls

38. Neuropsychology of Memory • HM, Hippocampal man • Dot pattern study (Gabrieli, 1990, Neuropsychologia, 28, 417-427) • Implicit memory – dot pattern priming equivalent for H.M. and controls • Explicit memory – H.M. impaired on recognition memory test compared to controls

39. Neuropsychology of Memory • HM, Hippocampal man • Dot pattern study (Gabrieli, 1990, Neuropsychologia, 28, 417-427) • Gabrieli and colleagues argued that this finding cannot be attributable to activation of a pre-existing memory (e.g., a semantic representation) • Proposed that it is attributable to a type of perceptual priming, perhaps of a non-semantic structural description of a pattern

40. Artificial grammar learning • Amnesics can have intact capacity for learning certain cognitive skills • E.g., artificial grammar such as shown in Figure • Participants were shown novel letter strings one at a time and were asked to classify the strings as grammatical or nongrammatical

41. Artificial grammar learning • Participants were then tested to determine whether they could distinguish between grammatical and nongrammatical letter strings • Results showed that amnesics and normal controls could classify correctly about two-thirds of the letter strings

42. Artificial Grammar • Top panel shows an example of an artificial grammar • Bottom panel shows examples of grammatical and nongrammatical strings • Knowlton et al. (1992). Psychological Science, 3, 172-179

43. Artificial grammar learning • Conclusions • Declarative memory and MTL not required to encode in memory those processes associated with the encoding into memory artificial grammars

44. Recognition memory: dual-process models • Several lines of evidence support the idea that two distinct processes (recollection, familiarity) mediated by different brain regions underlie recognition memory • Example. See face of a person – you recognize the person as familiar but are unable to recollect anything about the person, when or where you met that person • Recollection – you recognize that person and can recollect details about that person

45. Recognition memory: dual-process models • Evidence for dual process models (behavioral) • Speeded recognition tests have shown that item recognition tests (was this item studied) are made more quickly than associative recognition tests (when or where was this item studied) • Analysis of confidence intervals has shown that when hit rate is plotted against false alarm rate, curves are different for associative recognition (linear) versus item recognition (curvilinear) • also two different parameters are required to account for shape of curve suggesting that two distinctly different cognitive processes are operating

46. Recognition memory: dual-process models • Evidence for dual process models (behavioral) • Yonelinas has proposed that familiarity reflects the strength of the memory trace (an is quantitative) • Recollection reflects retrieval of qualitative, contextual information

47. Recognition memory: dual-process models • Evidence for dual process models (lesion) • Amnesics are much more impaired on associative recognition tests than on item recognition tests • Analysis of confidence intervals has shown that only 1 type of process (curvilinear) is required to account for recognition performance • See Yonelinas (2002) for further details

48. Neuropsychology of Memory • Functional characteristics of amnesia • working memory is intact • semantic memory is spared (controversial) • episodic memory is impaired • procedural memory is intact

49. Neuropsychology of Memory • Theoretical implications of amnesia • provides evidence for STM versus LTM distinction • supports the notion that there are different systems mediating explicit (episodic) and implicit (procedural memory) • may indicate that semantic and episodic memory can be fractionated • may provide insight into nature of consciousness

50. Neuropsychology of Memory • Memory and Consciousness • Tulving has proposed that different memory systems have associated with them different levels of consciousness • noetic -- awareness • episodic memory -- autonoetic, self awareness • semantic memory -- noetic, aware of the information, but not aware of event • procedural memory -- anoetic no conscious awareness