Activity of primate subgenual cingulate cortex neurons is related to sleep.

The most frequent type of neuronal response found in the subgenual cingulate cortex (area 25) of the rhesus macaque was a highly significant increase of firing rate when the monkey fell asleep (median rate = 1.6 spikes/s) compared with the awake state (median rate = 0.1 spikes/s). On average, the firing rate of the neurons when awake was 23% of that when the monkeys were asleep. Neurons were not found in this region with responses related to taste, olfactory, and visual stimuli including faces or related to movement. These results are relevant to understanding the function of this region in humans, in which it has been suggested that activation may be related to disengagement from tasks and to induced sadness, both of which we note lead to a more passive or resting behavior. A decrease in the activation of this area in humans has been observed during the recovery from depression, which we note leads to a more active state of behavior.