The neurology of confabulation
28 slide(s) – 00:22:57– English –2010-09-27
This lecture should enable attendees to understand that
- confabulations are not just verbal statements but may actually reflect precise underlying failures;
- there are different forms of confabulation with independent anatomical basis, clinical course, and causes;
- one precise form, called behaviorally spontaneous confabulation, has a distinct mechanism: the failure of a preconscious memory filter;
- orbitofrontal area 13 is critical for keeping thought an behavior in phase with reality.
Confabulation, the emergence of memories of events and experiences which in reality never took place, has puzzled clinicians for over a century. There are different forms, which partly of fully dissociate from each other, both functionally and anatomically: 1) simple provoked confabulations, i.e. intrusions in memory tests, which appear to be a normal response to a faulty memory; 2) momentary confabulations that patients produce in discussions or upon questioning; they probably have different mechanisms in different diseases; 3) fantastic confabulations that are illogical and nonsensical; they have been observed in confusional states, in severe dementia and untreated psychosis; 4) behaviourally spontaneous confabulations which reflect a confusion of reality in thinking, are often concordant with the patient's spontaneous behaviour, and which are associated with disorientation and amnesia. This form appears to result from an inability to distinguish between memories that pertain to ongoing reality and memories that do not. Diverse studies have indicated that the ability to make this distinction depends on area 13 of the orbitofrontal cortex, which filters upcoming memories according to their relation with ongoing reality even before their content is consciously recognized. OFC area 13 appears to make use of its extinction capacity –the ability to learn that a previously valid anticipation no longer applies- to exert this function. Thus, rather than invoking high-level monitoring functions, the human brain seems to make use of an ancient biological faculty, extinction, to keep thought and behaviour in phase with reality.