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When Your Memories Can No Longer Be Trusted

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You went to a wedding yesterday. The service was beautiful, the food and drink flowed and there was dancing all night. But people tell you that you are in hospital, that you have been in hospital for weeks, and that you didn’t go to a wedding yesterday at all. The experience of false memories like this following neurological damage is known as confabulation.

The reasons why patients experience false memories such as these has largely remained a mystery. Studies in amnesic patients have associated confabulation with damage to the orbital and ventromedial prefrontal cortices. However, neuroimaging studies have associated memory-control processes which are assumed to underlie confabulation with the right lateral prefrontal cortex.

A new study by Dr Martha Turner and colleagues at University College London offers some clues as to what might be going on. They used a confabulation battery to investigate the occurrence and localisation of confabulation in an unselected series of 38 patients with focal frontal lesions.

Twelve patients with posterior lesions and 50 healthy controls were included for comparison. Significantly higher levels of confabulation were found in the frontal group, confirming previous reports. More detailed grouping according to lesion location within the frontal lobe revealed that patients with orbital, medial and left lateral damage confabulated in response to questions probing personal episodic memory (PEM).

Patients with orbital, medial and right lateral damage confabulated in response to questions probing orientation to time (OT). Performance-led analysis revealed that all patients who produced a total number of confabulations outside the normal range had a lesion affecting either the orbital region or inferior portion of the anterior cingulate.

These data provide striking evidence that the critical deficit for confabulation has its anatomical location in the inferior medial frontal lobe. Performance on tests of memory and executive functioning showed considerable variability. Although a degree of memory impairment does seem necessary, performance on traditional executive tests is less helpful in explaining confabulation.

Martha S Turner, Lisa Cipolotti, Tarek A Yousry, Tim Shallice
Institute of Cognitive Neuroscience, University College London, London, UK.

Confabulation: Damage to a specific inferior medial prefrontal system.

Cortex. 2008 Jun ;44 (6):637-48 18472034 (P,S,E,B,D)

Confabulation, the pathological production of false memories, occurs following a variety of aetiologies involving the frontal lobes, and is frequently held to be underpinned by combined memory and executive deficits. However, the critical frontal regions and specific cognitive deficits involved are unclear. Studies in amnesic patients have associated confabulation with damage to the orbital and ventromedial prefrontal cortices. However, neuroimaging studies have associated memory-control processes which are assumed to underlie confabulation with the right lateral prefrontal cortex. We used a confabulation battery to investigate the occurrence and localisation of confabulation in an unselected series of 38 patients with focal frontal lesions. Twelve patients with posterior lesions and 50 healthy controls were included for comparison. Significantly higher levels of confabulation were found in the frontal group, confirming previous reports. More detailed grouping according to lesion location within the frontal lobe revealed that patients with orbital, medial and left lateral damage confabulated in response to questions probing personal episodic memory (PEM). Patients with orbital, medial and right lateral damage confabulated in response to questions probing orientation to time (OT). Performance-led analysis revealed that all patients who produced a total number of confabulations outside the normal range had a lesion affecting either the orbital region or inferior portion of the anterior cingulate. These data provide striking evidence that the critical deficit for confabulation has its anatomical location in the inferior medial frontal lobe. Performance on tests of memory and executive functioning showed considerable variability. Although a degree of memory impairment does seem necessary, performance on traditional executive tests is less helpful in explaining confabulation.

Written by huehueteotl

May 22, 2008 at 7:52 am

Posted in Neuroscience

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