Topographic studies on visual neurons in the dorsolateral prefrontal cortex of the monkey

The topographic distribution and organization of visual neurons in the prefrontal cortex was examined in alert monkeys. The animal was trained to fixate straight ahead onto a tinty, dim light spot. While he was fixating, we presented a stationary second light spot (RF spot) at various locations in the visual field and examined unit responses of the prefrontal neurons to the RF-spot stimulus. Many prefrontal neurons, especially those located in the relatively superficial layers of the cortex, responded with a phasic and/or tonic activation to the RF spot illuminating a limited extent of the visual field, a receptive field (RF) being so determined. The visual neurons were found to be widely distributed in the prearcuate and inferior dorsolateral areas. One hemisphere mainly represented the contralateral visual field. According to the location of the neurons in these areas, their visual properties varied with respect to RF eccentricity from the fovea and in size. The neurons located in the lateral part of the areas and close to the inferior arcuate sulcus had relatively small RFs representing the foveal and parafoveal regions. When the recording site was moved medially, the RFs became eccentric from the fovea and were larger. Then, the neurons located between the caudal end of the principal sulcus and the arcuate sulcus had RFs with a considerable eccentricity. The size of the RF became progressively larger for anteriorly located neurons and this occurred generally without a change in RF eccentricity. The visual neurons were not organized on a regular pattern in the cortex with regard to their RF direction (vector angle) from the foveal region. From these observations, we conclude, first, that the prearcuate and inferior dorsolateral areas of the prefrontal cortex are functionally differentiated so that the lateral area's function is related to central vision, while that of the medial area to ambient vision. Second, the RF representation on the cortex with loss of the vector relation may generate an interaction between separate objects in visual space and may subserve the control of attention performance.