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.

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Many neurons in the inferior dorsolateral area of the monkey prefrontal cortex showed sustained increases in discharge rates during continuous gazing at a tiny light spot that had a reward significance. These increases might depend upon stimulus factors (light target), behavioral factors (gazing) or both. In this report, we tried to separate these factors and to test the extent to which each factor might contribute to the neuronal reaction. Monkeys were trained to exhibit two kinds of behavior : 1) maintained gazing at a light target and 2) "gazing" behavior without a clear target. We then examined neuronal behavior in these two kinds of gazing behavior. During "gazing at target," many prefrontal neurons showed tonic activation ; thus the previous findings were confirmed. These neurons behaved in various ways in "gazing without target" : 1) some of the neurons were activated to the same extent as in "gazing at target" ; 2) many others also showed activation but with lower discharge rates; and 3) the rest of the neurons completely ceased activation. Such variation in discharge patterns may be interpreted as meaning that there is a continuous and graded difference among individual neurons in the dependence of their gaze-related activation upon a visible target. Then it seems that the stimulus factors are involved in a graded manner in generation of the activation, and further that other factors, probably behavioral ones, also contribute in part to it.Recent investigations have revealed that during delayed-response tasks many neurons in the prefrontal cortex exhibit increased discharge rates with various patterns. Activation is seen during the presentation of the pre-delay cue, the delay period and/or animals' responses upon cue presentation (FUSTER, 1973;KUBOTA et al., 1974). Such activation of prefrontal cortical neurons may be related to the choice and use of visual cues in delayed-response performance. However, the variety of activation patterns seen and the rather complex sequence of stimulus and behavioral events present in this task have impeded further analysis