Functional columns in superior temporal sulcus areas of the common marmoset.

Cortical areas in the superior temporal sulcus (STS) of primates have been recognized as a part of the 'social brain'. In particular, biological motion stimuli elicit neuronal responses in the STS, indicating their roles in the ability to understand others' actions. However, the spatial organization of functionally identified STS cells is not well understood because it is difficult to identify the precise locations of cells in sulcal regions. Here, using a small New World monkey, the common marmoset (Callithrix jacchus) that has a lissencephalic brain, we investigated the spatial organization of the cells responsive to other's actions in STS. The neural responses to movies showing several types of other's actions were recorded with multicontact linear-array electrodes that had four shanks (0.4 mm spacing), with eight electrode contacts (0.2 mm spacing) for each shank. The four shanks were penetrated perpendicular to the cortical surface. We found that STS cells significantly responded to other's goal-directed actions, such as when an actor marmoset was reaching for and grasping a piece of food. The response profiles to the movies were more similar between the vertically positioned electrodes than horizontally positioned electrodes when the distances between electrodes were matched. This indicates that there are functional columns in the higher-order visual areas in STS of the common marmoset.