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The Cognitive and Neuroanatomic Underpinnings of Confabulation

Memory retrieval and monitoring for veracity both appear to be defective, and confabulation requires damage to two different brain regions.

Confabulations are statements or actions, often strikingly bizarre or nonsensical, based on unintentional distortions of memory. The cognitive and neuroanatomic basis for confabulations has long been thought to involve both a failure of episodic memory and frontal lobe dysfunction, but the details of that failure and of the particular frontal regions involved have been unclear.

To examine the basis of confabulation in greater detail, researchers recruited four patients with spontaneous confabulations (three due to anterior communicating artery aneurysm rupture and one due to an anterior communicating artery aneurysm infarct), eight patients with anterior communicating artery aneurysm rupture who did not confabulate, and 16 healthy control subjects. To distinguish between two competing theories of confabulations, all participants underwent several memory tests. Some tests required subjects to make fine-grained temporal context distinctions (recalling exactly when something occurred). Other tests required them to make fine-grained context distinctions (including determining whether a false statement was plausible) without the temporal element.

Compared with controls, both groups of patients had difficulty with the hardest tasks, regardless of their temporal aspect. In another task that required recall of previously learned narratives without temporal context (e.g., the story of Cinderella), confabulating patients showed greater spontaneous confabulations than did nonconfabulators. They were also more likely to consider implausible statements to be true.

Neuroanatomically, patients with damage to ventromedial prefrontal cortex had distortions and inaccuracies of memory, but additional damage to orbitofrontal cortex was necessary for spontaneous confabulations to occur. Cognitively, the authors hypothesized, one function of ventromedial and orbitofrontal cortex is an intuitive "feeling of rightness" that allows healthy individuals to reject memories that simply do not make sense. They suggest that this feeling of rightness is defective in people who confabulate.

Comment: Understanding the cause of confabulations is of great interest. Although patients with rupture of an anterior communicating artery aneurysm are relatively rare — and only a subset of these patients confabulate — patients with Alzheimer disease frequently exhibit memory distortions and sometimes show outright confabulations (Neuropsychology 2004; 18:315). This series of elegant experiments sheds light on which neuroanatomic regions and cognitive components may be dysfunctional in patients with Alzheimer disease who exhibit memory distortions and confabulations.

— Andrew E. Budson, MD

Dr. Budson is Associate Professor of Neurology, Boston University School of Medicine; Director of Cognitive Neuroscience Research, Boston University Alzheimer’s Disease Center; Associate Clinical Director, Geriatric Research Education Clinical Center, Edith Nourse Rogers Memorial Veterans Hospital; Lecturer in Neurology, Harvard Medical School; and Associate Neurologist, Division of Cognitive and Behavioral Neurology, Department of Neurology, Brigham and Women’s Hospital, Boston.

Published in Journal Watch Neurology July 25, 2006

Citation(s):

Gilboa A et al. Mechanisms of spontaneous confabulations: A strategic retrieval account. Brain 2006 Jun; 129:1399-414.

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