New Kind Of Brain Activity Found Beyond EEG 'Flat-lined' Deep Coma

Scientists say they’ve discovered a totally new kind of brain activity lurking beyond the “flat-lined” state seen in deep comas.

A team of Canadian and Romanian researchers found evidence of cerebral activity both in a human coma patient and in 26 cats induced by drugs into an incredibly deep (but reversible) coma. They describe the new phenomenon, which they’ve dubbed “Nu-complexes,” in a paper published Wednesday in the journal PLoS ONE.

Initial stages of comas are comparable to deep sleep, but if a person progresses into a deeper and deeper quietude, the brain state alters more dramatically. In cases of very deep comas, an electroencephalogram (EEG) monitor will render a flat line (also called an isoelectric line), marking a state in which the brain’s electrical activity has either stopped or is so low it is virtually undetectable. This is considered one of the boundary lines between having a living brain and brain death, but is not the only criteria that doctors use to declare someone brain-dead; there usually has to be evidence of structural damages in the brain as well.

This new research suggests that cerebral activity can revive after the flat-lined state, under certain conditions. The work started when Romanian doctor and study coauthor Bodan Florea observed unusual brain activity in a hospital patient who went into a coma following a heart attack.

Florea and two University of Montreal researchers decided to try and re-create the human patient’s brain state in animals. They pushed laboratory cats to the flat-lined state with an anesthetic called isoflurane. When they gave the cats doses of the drug even higher than the amount that induces a flat EEG line, they saw “a re-vitalization of activity in the brain,” marked by the appearance of sharp EEG waves in all 26 subjects. The brain activity revealed itself to be oscillations stemming from the hippocampus -- a brain area associated with memory and learning -- and sent to the cortex. The team believes these waves, or Nu-complexes, match the brain state of the human patient.

“Nu-complexes appear in a deeper state of coma, provided that neurons are well-fed, well-supplied with blood and oxygen and in good shape,” senior author Florin Amzica said in a phone interview.

The find, Amzica says, is a new frontier in brain research. There are still many remaining questions about the kind of extra-deep coma that gives rise to Nu-complex. It is even possible that this kind of brain activity might even keep a brain from “atrophying” after a long period of coma.

“We want to know if this state is beneficial for the brain,” Amzica says. Though “at this point we don’t know if any [brain] modifications are set into motion by such a deep coma.”

However, the team wants to caution people not to interpret their study as a sign that, perhaps, one’s brain-dead relative was actually alive.

"Those who have decided to or have to 'unplug' a near-brain-dead relative needn't worry or doubt their doctor,” Amzica said in a statement. “The current criteria for diagnosing brain death are extremely stringent. Our finding may perhaps in the long term lead to a redefinition of the criteria, but we are far from that. Moreover, this is not the most important or useful aspect of our study.”

SOURCE: Kroeger et al. “Human Brain Activity Patterns beyond the Isoelectric Line of Extreme Deep Coma.” PLoS ONE published 18 September 2013.