Delay-period Activity in the Prefrontal Cortex: One Function Is Sensory Gating

The prefrontal cortex (PFC) contributes to working memory functions via executive control processes that do not entail the storage, per se, of mnemonic representations. One of these control processes may be a sensory gating mechanism that facilitates retention of representations in working memory by down-regulating the gain of the sensory processing of intervening irrelevant stimuli. This idea was tested by scanning healthy young adults with functional magnetic resonance imaging while they performed a delayed face-recognition task. The 2 × 2 factorial design varied the factors of Memory (present, absent) and Distraction (present, absent). During memory-present trials, target and probe stimuli were individual gray-scale male faces. Memory-absent trials were identical, except that they employed the same recurring female faces (denoting a “no memory” trial). Distraction-present trials featured rapid serial visual presentation of bespectacled male faces during the two middle seconds of the delay. The first step of the analyses identified dorsolateral PFC (dlPFC) and inferior occipitotemporal cortex (IOTC) voxels exhibiting delay-period activity in memory-present/distraction-absent trials, that is, the “unfilled” delay. Within these voxels, distraction-evoked activity in the dlPFC was markedly higher during trials that required the concurrent short-term retention of information than on those that did not, whereas the opposite effect was seen in the IOTC. These results are consistent with the view that processes related to sensory gating account for a portion of the delay-period activity that is routinely observed in the dlPFC.