Laminar architecture of visual responses in supplementary eye field of macaques

Previously, we have described the laminar organization of neurons in the supplementary eye field (SEF) that signal error, reward gain and loss, conflict, event timing, and goal maintenance. Here we describe the laminar organization of visually responsive neurons that were active during performance of a saccade stop-signal task. Nearly 40% of isolated neurons exhibited enhanced or suppressed responses to a visual target for a potential saccade, with the majority exhibiting enhanced activity and three-quarters with broad spikes. Visually responsive neurons were observed in all layers but were less common in layers 5 and 6. Response latencies were comparable to those reported previously, which are significantly later than those measured in occipital and temporal visual areas but overlapping those measured in cingulate cortex. Task-related visual response latency varied across cortical layers. Response latency was significantly earlier for neurons with narrow spikes. Neurons with task-related visual responses discharged until after saccade production. Around three-fifths of visually responsive neurons were most sensitive to the visual target appearing in one hemifield. Many neurons in layer 2 had ipsilateral receptive fields. Laminar current-source density aligned on visual target presentation revealed the earliest sink in layers 3 followed by a prolonged strong sink more superficially coupled with a weaker prolonged sink in layer 5 and a transient sink in layer 6. The current sink in layers 2 and 3 was stronger for ipsilateral stimuli. These findings reveal new details about visual processing in medial frontal cortex and complete the first catalogue of laminar organization of functional signals in a frontal lobe area.