The loss and return of consciousness are linked to the same network of brain regions for both sleep and anaesthesia, according to new research published in the  Journal of Neuroscience.

The biological basis of consciousness has confounded scientists for centuries. Our experimental techniques falter, as the effects of sleep and anaesthetic drugs alter brain activity beyond changes in consciousness. In addition, behaviour does not always reveal someone’s state of consciousness. An unresponsive person might still be aware of their surroundings (connected), or unaware but still experiencing their internal world (disconnected).

Scheinin and colleagues sought networks associated with human consciousness by measuring the brain activity of adult males with PET as they fell asleep and went under anaesthesia.

The research team woke participants mid-experiment to interview them and confirm their state of connectedness. Changes in connectedness corresponded to the activity of a network comprised of regions deep inside the brain: the thalamus, anterior and posterior cingulate cortex, and angular gyri. These regions exhibited less blood flow when a participant lost connectedness and more blood flow when they regained it.

The pattern held true for both sleep and anaesthesia, indicating the changes corresponded to connectedness rather than the effects of sleep or drugs, and that the network may be imperative for human consciousness.