Differential characteristics of face neuron responses within the anterior superior temporal sulcus of macaques.

The anterior superior temporal sulcus (STS) of macaque monkeys is thought to be involved in the analysis of incoming perceptual information for face recognition or identification; face neurons in the anterior STS show tuning to facial views and/or gaze direction in the faces of others. Although it is well known that both the anatomical architecture and the connectivity differ between the rostral and caudal regions of the anterior STS, the functional heterogeneity of these regions is not well understood. We recorded the activity of face neurons in the anterior STS of macaque monkeys during the performance of a face identification task, and we compared the characteristics of face neuron responses in the caudal and rostral regions of the anterior STS. In the caudal region, facial views that elicited optimal responses were distributed among all views tested; the majority of face neurons responded symmetrically to right and left views. In contrast, the face neurons in the rostral region responded optimally to a single oblique view; right-left symmetry among the responses of these neurons was less evident. Modulation of the face neuron responses according to gaze direction was more evident in the rostral region. Some of the face neuron responses were specific to a certain combination of a particular facial view and a particular gaze direction, whereas others were associated with the relative spatial relationship between facial view and gaze direction. Taken together, these results indicated the existence of a functional heterogeneity within the anterior STS and suggested a plausible hierarchical organization of facial information processing.