Disconnecting part of the brain sends it into a deep sleep

"The team wanted to find out whether the disconnected part has some form of awareness - or was capable of exhibiting consciousness, says co-author Marcello Massimini, a neurophysiology researcher at the University of Milan in Italy. "The question arises because we have no access" to the disconnected region, he says, adding that it was unclear what happens once part of the brain is isolated."

"Studies investigating consciousness are difficult because there is no consensus on what conscious and unconscious states in the brain look like, says Ariel Zeleznikow-Johnston, a neuroscientist at Monash University in Melbourne, Australia. "There's no generally accepted definitive signatures of consciousness in terms of electrical readings or brain activity," he adds. Even defining unconsciousness is challenging, because activities associated with consciousness, such as remembering dreams, can occur during states associated with unconsciousness, such as sleep or anaesthesia, Massimini says."

Slow, sleep-like brain waves persist in parts of the brain that have been surgically disconnected from the rest of the organ, occurring even when patients are awake. Children with severe, drug-resistant epilepsy can receive a hemispherotomy that severs connections but leaves the isolated tissue intact and vascularized. EEG comparisons before and months to years after surgery examined residual electrical activity in the disconnected hemisphere. Persistent slow oscillations in isolated tissue complicate simple mappings of electrophysiological patterns to conscious or unconscious states. Defining consciousness using electrical signatures remains uncertain because sleep-like activity and dream-related processes can overlap with wake-associated phenomena.

Read at Nature