A 1–3-Hz rhythm in deep posteromedial cortex underlies dissociative states in both mice and humans. In mice, precisely-dosed ketamine or phencyclidine induced this rhythm in layer 5 neurons of the retrosplenial cortex, which coupled with thalamus circuitry but uncoupled from most other brain regions. Rhythmic optogenetic activation of these neurons recapitulated dissociation-like behaviors. Local HCN1 pacemakers were required for ketamine to induce the rhythm and behavioral effects. In a patient with focal epilepsy, a similar localized rhythm in the homologous deep posteromedial cortex correlated with pre-seizure self-reported dissociation, and electrical stimulation of this region elicited dissociative experiences.
Electrical stimulation of the posteromedial cortex (PMC) can induce a temporary sense of self-dissociation—a distorted awareness of one's body in space and feeling like an outside observer to one's own thoughts. A patient with seizures originating in the right dorsal posterior cingulate cortex (Brodmann area 31) reported this reproducible experience at seizure onset. Stimulating the seizure zone or a homotopical region in the left PMC at 50 Hz induced a subjectively similar state. The findings suggest a causal link between the PMC and the integration of self-referential information, offering clues about the pathophysiology of self-dissociation in neuropsychiatric conditions.