Single unit responses in the lateral prefrontal cortex reflect trial phase dependent modulation

Neuronal responses in the lateral prefrontal cortex (LPFC) of the macaques engaged in various behavioral paradigms exhibit a large diversity of patterns underlying multiple cognitive functions ranging from working memory to serial order and even visual awareness. We have previously examined single unit activity in the LPFC with an ambiguous visual stimulation paradigm called binocular flash suppression in order to understand its role in conscious visual perception. We observed feature selective visual responses among 11 percent of the recorded neurons. The present study aimed at elucidating any other dominant pattern among the remaining majority of single units. We therefore clustered the peristimulus time histograms of remaining neurons with a non-negative matrix factorization procedure. This led to the identification of five major response patterns whose peak amplitude was distributed chronologically across different phases of a trial. Moreover, majority of single units displaying activity similar to a given response pattern did not exhibit significant difference in their responses during the monocular and binocular conditions of the task, thus suggesting that their firing was unaffected by ambiguous visual input. We therefore report the existence of temporally contingent trial phase dependent spiking activity among single neurons during a passive fixation paradigm which does not require any explicit mnemonic demands or a behavioral report associated motor action. In addition, this trial phase preference activity remains unchanged across monocular or binocular conditions thus supporting the existence of a neural process, unaffected by incongruent visual stimulation and most likely related to tracking the progress of a trial