Neural overlap between resting state and self-relevant activity in human subcallosal cingulate cortex--single unit recording in an intracranial study.

High activity of the default mode network (DMN) has been proposed to be central in processing self-relevant events. Thus far, this hypothesis of DMN function has not been tested directly using neurophysiological techniques. To test for the link between frontal midline DMN activity and self-relevant processing we measured neuronal activity (single-neurons' firing rates) in human subcallosal cingulate cortex (SCC) in the course of Deep Brain Stimulation surgery. We find that firing rates in SCC did not change during the presentation of specifically self-relevant stimuli when compared to the preceding pre-stimulus resting state level. In contrast, we observed significant changes in firing rates during other names in SCC. Such rest-self overlap seems to be specific for SCC since increase in firing rates in response to self-relevant stimuli were observed in another region, the subthalamic nucleus, in a group of Parkinson patients receiving deep brain stimulation surgery. These results suggest specific relationship between resting state and self-related activity, rest-self overlap, in specifically SCC as core region of the default-mode network.