CONTRIBUTION OF HUMAN PREFRONTAL CORTEX TO DELAY PERFORMANCE

Neurological patients with focal lesions in the dorsolateral prefronta l cortex and age-matched control subjects were tested on an auditory v ersion of the delayed-match-to-sample task employing environmental sou nds. Subjects had to indicate whether a cue (S1) and a subsequent targ et sound (S2) were identical. On some trials, S1 and S2 were separated by a silent period of 5 sec. On other trials, the 5-sec delay between S1 and S2 was filled with irrelevant tone pips that served as distrac tors. Behaviorally, frontal patients were impaired by the presence of distractors. Electrophysiologically, patients generated enhanced prima ry auditory cortex-evoked responses to the tone pips, supporting a fai lure in inhibitory control of sensory processing after prefrontal dama ge. Intrahemispheric reductions of neural activity generated in the au ditory association cortex and additional intrahemispheric reductions o f attention-related frontal activity were also observed in the prefron tal patients. Together, these findings suggest that the dorsolateral p refrontal cortex is crucial for gating distracting information as well as maintaining distributed intrahemispheric neural activity during au ditory working memory.