Dissociation is the feeling of disconnecting from your surroundings or sense of self. It is associated with several psychiatric illnesses and with club drugs like ketamine. But dissociation is an inherently personal experience, and scientists have historically struggled to study how the brain manifests it.
A September 2020 study published in Nature employed an impressive lineup of cutting-edge tools to address this impossible question: how can our brains disconnect us from ourselves?
Neuroscientists identified slow brain waves in the retrosplenial cortex, a key player in learning, imagination, and autobiographical memory, as a hallmark of dissociative states. They injected mice with sub-anesthetic doses of ketamine to induce dissociation, then peered into their brains through their transparent skulls. After ketamine injection, an unusual, slow brain wave emerged in the retrosplenial cortex, oscillating at about 2 Hz (the same beat as Carly Rae Jepsen’s Call Me Maybe).
Using light to stimulate genetically-modified neurons in the retrosplenial cortices of the mice, they recreated the same beat, sending the mice into a dissociative-like state without any drugs at all. A specific ion channel, HCN1, seems to be responsible for setting the tempo of these dissociation-linked brain waves.
And it’s not just mice. A human epilepsy patient, who regularly experienced pre-seizure dissociative auras, demonstrated the same brain waves in the same region identified in mice. When researchers elicited the beat via electrical stimulation, the patient reported dissociative episodes: “...the same way a pilot can lose control of a plane, I got pulled out of the pilot’s chair, but I could still see all the gauges.”
When a group of neurons oscillates on the same wavelength as another group, it’s easier for them to communicate. Dissociative slow brain waves seemed to decouple the brain regions implicated in forming our sense of self from those required for perceiving, planning, and action.
Moving forward, the technology used here may equip scientists to dive deeper into the study of consciousness, helping us understand how the brain creates the mind.