Spontaneous confabulators fail to suppress currently irrelevant memory traces

Human actions require integration of past experiences, ongoing percepts and future concepts. To adapt behavior to reality, the brain must identify men tal representations of current relevance. Occasional amnesic subjects act a ccording to invented stories ('spontaneous confabulations'), disregarding p resent reality. We used repeated runs of a continuous recognition task to m easure the ability to distinguish currently relevant from previously encoun tered but currently irrelevant information. Spontaneous confabulators detec ted target items as accurately as nonconfabulating amnesics, but increasing ly failed to suppress false-positive responses, confusing presentation in p revious runs with presentation in the current run. Lesions involved the ant erior limbic system: medial orbitofrontal cortex, basal forebrain, amygdala and perirhinal cortex or medial hypothalamus. We suggest that the anterior limbic system represents 'now' in human thinking by suppressing currently irrelevant mental associations.