Nature looks at dissociative states, and the specific rhythm in a single layer of neurons that can make everything around you seem unreal:
The neurological basis of dissociation has been a mystery, but writing in Nature, Vesuna et al. 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 navigation. 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.
Vesuna and colleagues recorded electrical activity from several brain regions in a person with epilepsy, who had previously had electrodes implanted in their cranium to locate seizure activity. The individual experienced dissociation before the onset of seizures. The authors found that this dissociation correlated with a 3-Hz rhythm in the deep posteromedial cortex — a human brain region analogous to the mouse retrosplenial cortex. When the team electrically stimulated the deep posteromedial cortex during a brain-mapping procedure, the person again experienced dissociation.
Rapid technological advances are producing increasingly sophisticated techniques to manipulate neural circuits with precision and high temporal resolution. Vesuna and colleagues’ work exemplifies how these advances are enabling investigators to probe the nature of consciousness itself. They are also revolutionizing the science of anaesthesiology — allowing investigators to better understand how anaesthetics produce unconsciousness, how these mechanisms overlap with natural sleep, and how people recover consciousness after anaesthesia.