The brain rhythms that detach us from reality
The state of dissociation is commonly described as feeling detached from reality or having an ‘out of body’ experience. This altered state of consciousness is often reported by people who have psychiatric disorders arising from devastating trauma or abuse. It is also evoked by a class of anaesthetic drug, and can occur in epilepsy. The neurological basis of dissociation has been a mystery, but writing in Nature, Vesuna et al.1 describe a localized brain rhythm that underlies this state. Their findings will have far-reaching implications for neuroscience. The authors first recorded brain-wide neuronal activity in mice using a technique called widefield calcium imaging. They studied changes in these brain rhythms in response to a range of drugs that have sedative, anaesthetic or hallucinogenic properties, including three that induce dissociation — ketamine, phencyclidine (PCP) and dizocilpine (MK801).
Only the dissociative drugs produced robust oscillations in neuronal activity in a brain region called the retrosplenial cortex. This region is essential for various cognitive functions, including episodic memory and navigation2. The oscillations occurred at a low frequency, of about 1–3 hertz. By contrast, non-dissociative drugs such as the anaesthetic propofol and the hallucinogen lysergic acid diethylamide (LSD) did not trigger this rhythmic retrosplenial activity.