Unmasking of silent "task-related" neuronal activity in the monkey prefrontal cortex by a GABA(A) antagonist.

To examine the role of GABA on prefrontal neuronal activity in the control of behavior, a GABA(A) receptor antagonist, bicuculline methiodite (BMI), was iontophoretically applied to prefrontal neurons while monkeys performed a visual reaction time task. Iontophoretic application of BMI uncovered "task-related" activity of silent neurons (n=40), which did not show any activity during performance of the task. The distribution, by type, of these silent "task-related" neurons differed from that of standard (i.e. active) task-related neurons (N=95), and a particular type of silent "task-related" neuron was found most frequently. These findings suggest that GABA continuously and preferentially suppresses neuronal activity via GABA(A) receptors to limit the population of prefrontal neurons related to behavior, thereby organizing neuronal activities for behavior mediated by the prefrontal cortex.