Shape selectivity in primate frontal eye field.

Previous neurophysiological studies of the frontal eye field (FEF) in monkeys have focused on its role in saccade target selection and gaze shift control. It has been argued that FEF neurons indicate the locations of behaviorally significant visual stimuli and are not inherently sensitive to specific features of the visual stimuli per se. Here, for the first time, we directly examined single cell responses to simple, two-dimensional shapes and found that shape selectivity exists in a substantial number of FEF cells during a passive fixation task or during the sample, delay (memory), and eye movement periods in a delayed match to sample (DMTS) task. Our data demonstrate that FEF neurons show sensory and mnemonic selectivity for stimulus shape features whether or not they are behaviorally significant for the task at hand. We also investigated the extent and localization of activation in the FEF using a variety of shape stimuli defined by static or dynamic cues employing functional magentic resonance imaging (fMRI) in anesthetized and paralyzed monkeys. Our fMRI results support the electrophysiological findings by showing significant FEF activation for a variety of shape stimuli and cues in the absence of attentional and motor processing. This shape selectivity in FEF is comparable to previous reports in the ventral pathway, inviting a reconsideration of the functional organization of the visual system.