Previous studies indicated that the anterior cingulate cortex (ACC) is one of the critical brain areas for social behaviors, and that the effects of PCP might be mediated through the ACC. However, few studies investigated neural correlates with social behaviors in the ACC. To investigate this issue, the authors recorded ACC neuronal activity from one of the 2 monkeys while these 2 monkeys socially interacted. The results indicated that activity of some neurons was significantly correlated with one or more of social behaviors. Activity of leaving- and approaching-related neurons changed in response to leaving and approaching behaviors of recording and/or partner monkeys, respectively. Activity of the communication-related neurons changed while the 2 monkeys engaged themselves in a series of social behaviors such as grooming together, lip smacking, facing, etc. These results provide neurophysiological basis for ACC involvement in psychiatric disorders with social disturbance such as schizophrenia, austism...