Laminar organization of neuronal activities in area 8 of rhesus monkeys during a symmetrically reinforced visual GO/NO-GO task.

An attempt was made to clarify the laminar distributions of neurons activated during a symmetrically reinforced, visually guided GO/NO-GO task with visual cues for which Brodmann's area 8 (Walker, 1940) is considered an essential region (cf. Petrides, 1986). We systematically recorded single unit activities in area 8 in 200 microns steps from the surface to the bottom of the cortex, using a glass-coated microelectrode that contained a carbon fiber. The GO/NO-GO task consisted of four periods in sequence: an intertrial interval (ITI; waiting period, warning period (which started with a warning cue), GO/NO-GO period (which started with a GO/NO-GO cue), and reward period. Activities of GO cue-coupled neurons, intermediate neurons and movement-coupled neurons in GO trials were recorded in layers II-VI, layers II-VI and layers III-VI of the area 8, respectively. Activities of NO-GO cu-coupled and NO-GO response-related neurons in NO-GO trials were recorded in layers II-VI and layers III-VI, respectively. It was considered that task-related visual information may be fed to layer III and IV, as a GO/NO-GO cue coupled activity, and then flow upward and/or downward to layers III-VI where movement-coupled activities are recorded. NO-GO response-related activity appears to suppress GO activity in layers III-VI. It was noted that the laminar distribution of NO-GO response-related neurons was similar to that of movement-coupled neurons in GO trials, and that the shape of spikes of NO-GO response-related neurons in our study resembled that of spikes of putative GABAergic neurons in a previous study. These results suggest that NO-GO response-related neurons are involved in response inhibition through GABAergic mechanisms.