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 last 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 • 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)

7. 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

8. 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

9. Neuropsychology of Memory

10. 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

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. • How can someone with a shattered memory remember that he has become unable to remember?

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 (covered?)

26. Neuropsychology of Memory • Multiple memory systems perspective • HM also has 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 is able to recall it • This finding suggests that the medial temporal lobes are not always required to retrieve memories (One possibility is that some process occurs that makes it possible to retrieve information that does not rely on medial temporal lobes) • Long-term memory consists of all the different types of memory shown in the previous slide • Explicit (declarative) memory refers to memory that can be declared or described to other people • It includes episodic memory, memory for events in our personal past. Episodic memories are temporally dated, spatially located, and personally experience • semantic memory, our general knowledge about things in the world

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 from 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 tasks

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