Wednesday, May 27, 2009

Confabulatory Hypermnesia

Neurophilosophy has a report on an article in Cortex1 about a man who confabulates (describes fictitious events to fill in gaps in memory) extensively and continuously as a result of amnesia:

LM confabulated plausible answers to questions about both his personal life and public events, which would normally elicit from most people an answer of "I don't know". When the researchers asked him "Who won the Palme d'Or at the Cannes Film Festival in 1980?" he replied "Fernandel"; when asked what he had for dinner on Tuesday two weeks ago, he answered "Steak with french fries"; and when asked "Do you remember what you did on March 13th, 1985?" he replied "We spent the day at the Senart Forest."

LM thus has a "pure" amnesic syndrome, in that his impairment is not associated with other cognitive deficits which might interfere with memory function. He scored normally on short-term memory tests, and the evaluation revealed mild, diffuse neurodegeneration, rather than damage in a specific part of the brain. False memories are not uncommon in patients with Korsakoff's syndrome - indeed the condition is also referred to as amnesic-confabulatory syndrome. However, the confabulations of such patients are sometimes extraordinary, bizarre and verging on being delusional. LM's confabulations, on the other hand, were always plausible, and therefore quite unlike those reported in other Korsakoff's patients.

...So how might LM's amnesic syndrome arise? The authors explain it within the framework of the memory, consciousness and temporality theory. According to this theory, consciousness always relates to "something", such as an object or event, and does not exist as a unitary dimension, but rather as a distinct set of "modes" for addressing the "thing" of which one is conscious of at any given moment. These modes include knowing consciousness and temporal consciousness, which describe, respectively, knowing the object of consciousness and placing it somewhere on the timeline of past, present and future.

For example, a pen is a pen and a meal is a meal, and each can be lumped together with others into the same category. But at a given moment, one might be conscious of the pen sitting on a table, or of the meal that has just been eaten. Thus, every object or event which enters consciousness has both a multiplicity and a uniqueness. The authors suggest that LM may be unable to distinguish between these two properties. His temporal consciousness is present, but working abnormally. It has become "expanded", so that while he can retrieve information about personal events and habits, the particulars of a specific object of consciousness are applied to all the objects within that category, and they become confused with one another.

1 Dalla Barba, G., & Decaix, C. (2009). "Do you remember what you did on March 13, 1985?" A case study of confabulatory hypermnesia. Cortex 45: 566-574. DOI: 10.1016/j.cortex.2008.03.009.
(via boingboing)

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