Ventromedial prefrontal cortex lesions produce early functional alterations during remote memory retrieval

Abstract

We examined the role of ventromedial prefrontal cortex (VMPFC) in memory retrieval monitoring. Event-related potentials were recorded while patients with VMPFC lesions and matched controls viewed faces of personal acquaintances, and of famous and nonfamous people, and indicated whether they had personally encountered these individuals. Patients were more likely than controls to make both false positive and false negative errors. Both groups showed a large posterior negative wave peaking at ~170 ms after face onset (N170). In controls, the N170 was larger for both types of familiar faces, regardless of whether overt recognition occurred. Specifically, personal acquaintances that were erroneously judged as unfamiliar evoked the same Electro physiological response as those who were explicitly recognized. Patients' N170 was not modulated by familiarity suggesting VMPFC lesions disrupt early posterior memory-based precon-scious cortical distinctions. Following the N170, there was a significant group difference over frontopolar scalp regions where patients were showing a smaller positive modulation at 230-260 ms for all stimulus types. In patients this modulation correlated highly with reaction times of correct responses, suggesting this early frontal modulation is related to the ability to make rapid correct decisions about memory content. Group differences over anterior sites were also noted at 350 ms after stimulus, reflecting a large sustained negativity of patients' waveforms, equal across conditions. The findings are consistent with a hypothesis of frontally mediated dual-monitoring system. An early automatic (preconscious) component is followed by a late elaborate process. We hypothesize that when both components are damaged, confabulation may occur. Copyright © 2009 Society for Neuroscience.