Week 4 - Amnesia

who is Patient H.M.? The removal of which section of his brain causes memory deficits? what type of memory deficits were caused by the removal of said brain section?

• HM suffered from intractable epilepsy since age 7

  • Neurosurgeon William Scoville localized HM’s epilepsy to his medial temporal lobe and suggested surgical resection

  • In 1953, parts of HM’s MTL were removed from both sides of his brain

• Type of Memory of Deficits

  • memory from weeks and years preceding the surgery were intact

  • HM could not form new long-term declarative memories (anterograde amnesia)

  • all other aspects of intellectual functioning were preserved

what examples were given of the informal testing conducted on patient HM?

• Employment

  • HM was given protected employment after the passing of his father. He was unable to give any description of his place of work, the nature of his job, or the route along which he is driven each day

• Navigation to Address

  • He was unable to direct the researchers to his current place of residence. Instead, he directed them to a street where he lived prior to his operation.

• Language

  • His comprehension of language is undisturbed. He can repeat and transform sentences with complex syntax, and he gets the point of jokes, including those turning on semantic ambiguity

what examples were given of the formal testing conducted on patient HM?

• Block Test

  • Patient was capable of recreating image by rearranging blocks to mirror the image presented

• Mooney Face Test

  • Subject has to detect a face from a block and white patient with incomplete contour

  • He was capable of doing this

• Short-Term Memory

  • He can functioning short term memory in a test where he is asked to repeat four different words

• Ray-Osterreith Complex FIgure

  • Copy: copy the ROCF onto paper while looking

  • Immediate Recall: examine figure, figure taken awar, reproduce from meory

  • Delayed Recall: Examine figure, figure taken away, 20 - 30 min delay, reproduce from memory

how does Patient HM perform on the ROCF testing?

• He can copy just fine

• He struggles with delayed recall (literally comes up blank)

how did the case of Patient HM reform memory models? what were three important revelations came from HM?

• we learned that the hippocampus and the medial temporal lobe are critical for making new memories

• his procedural memories were intact

• he suffered from temporally graded retrograde amnesia

• what are some features of nondeclarative memory / procedural memory?

• what are some tests of procedural memory?

• Memories that you don’t remember through retrieval cue. They are memories in which you must do the task in order to see if you still have the ability

• Tests include . . .

  • Mirror drawing task

  • Repetition Priming

  • Visual Search

what is the mirror drawing task? how did HM do on this task? what does his performance tell you about his memory deficits? can HM recall ever doing the task?

• trace figure while looking in a mirror

• control subjects get better at this with repetitive training

• HM performance

  • improved with repeated training

  • shows that procedural memory is intact

• No, HM cannot recall ever having performed this task before (no declarative memory for having performed the task)

HM doesn’t have a hippocampus. Considering HM’s progression in the mirror drawing task, what does this indicate about his type of memory and the involvement of the hippocampus?

• Conclusion

  • procedural memories DO NOT involve the hippocampus

what is the repetition priming task? how does HM perform on this task? why are the results interesting?

• Definition:

  • the subject examines a list of words

  • following examination, the subject is asked to fill in the blanks (the first word that comes to mind)

• Patient HM Results

  • Patient HM shows repetition priming

  • this is interesting because HM has no recollection of the words on the original list

• what is the visual search task?

  • is this generalizable?

• how long can you retain improved visual search task skill?

• what’s an interesting fact about this study?

• how does HM perform on this task?

• Definition:

  • flashed grid of a bunch of triangles

  • subject is asked if they saw an upside-down triangle in the grid

  • performance assessment based off of correct trials

  • subjects have no conscious perceptual distinction between different triangles, despite having better performance for target triangles

• Generalizability

  • NO

  • switching to up-right triangle will have poor performance

• How long does he last?

  • like a month (sheesh)

• Patient HM Results

  • yes, they can improve at this task.

what are some features of the task that test procedural memory? are there any similarities between these different tasks that can help us draw conclusions about these “procedural” memories?

• Procedural Memory Tasks

  • showcases a type of non-conscious memory

  • must do task to figure out if you have memory

Fill in the blank. What are the implications of this statement for non-conscious learning and conscious learning?
Perceptual learning is both _____________ & ______________.

• Perceptual learning is both non-conscious and extremely specific

  • improved ability to detect one target does not transfer to another target (learning is extremely specific, think visual search task)

• Implications

  • non-conscious (procedural) learning involves neurons in visual cortex

  • conscious (declarative) learning requires the hippocampus

what is the difference in uptake speed in hippocampal neurons vs. cortex neurons?

• Hippocampal neurons

  • fast uptake speed

• Cortex Neurons

  • slower uptake speed

  • more resistant to learning

  • shown by numerous trials in order to improve ability in specific tasks

• what two types of amnesia did patient HM have?

• what does it mean to have temporally graded amnesia?

• what do the different types of amnesia imply about how we form memories?

• Severe Anterograde Amnesia: loss of memory for events following the lesion

  • Implication: the hippocampus is needed to form new memories

• Temporally Graded Retrograde Amnesia: loss of memory for some events preceding the lesion

  • amount of memory loss is determined by the amount of time you are away from the lesion

  • Implication: the hippocampus plays a role in consolidating memories in the cortex for some period of time after the memory is first formed

what are the implications of how memory processes work (or how the hippocampus works) if HM lost memories of the recent past post-surgery despite having a hippocampus at the time of those events?

• It takes time for memory to consolidate

• Hippocampus plays a role in retrieval of memory