Sawaguchi ToshiyukiNeuroReport: December 30th, 1994 Original Article: PDF Only Abstract To examine functional local connections in the primate neocortex, we examined changes in optical signal by intra-cortical microstimulation (ICMS), using a voltage-sensitive dye (RH795) in frontal, and parietal cortical areas of the anaesthetized monkey. ICMS increased the optical signal at the stimulated site, followed by increases, and decreases in a modular fashion at regions that were from hundreds of micrometres to a few millimetres from the stimulated site. These changes lasted for 100–250 ms after the offset of ICMS. Further, this increase in the optical signal was accompanied by an increase in electrical activity in the neurones. These findings suggest the presence of excitatory, and inhibitory modular connections within the neocortical areas. It is likely that some functional ‘modules' are activated concurrently by excitatory loops, which suppress the activity of other modules. © Lippincott-Raven Publishers.