Traces of Life

Researchers identify previously unrecognized neuronal activity in comatose human and feline brains.

By | September 24, 2013

FLICKR, EUSKALANATOOne criterion generally used to determine brain death is a flat or isoelectric electroencephalogram (EEG) trace. But new research published last week (September 18) in PLOS One showed that neuronal activity can be detected when the brain is in an extreme deep coma, even after an EEG has flatlined.

Researchers from the University of Montreal observed previously unreported spikes of neuronal activity, which they called Nu-complexes, in the EEG of one human patient in a deep coma. In order to see whether they could recreate the Nu-complexes in the lab, the researchers subjected cats to increasing amounts of anesthesia, putting each animal into a reversible, drug-induced coma. At a medium-high dose of anesthesia, the cats’ EEG traces flatlined, but when the scientists increased the dose of anesthesia even more, they saw Nu-complexes in each cat’s EEG. The researchers then pinpointed the origin of the Nu-complexes to the hippocampus.

Because a flat EEG is usually used in combination with other clinical indicators to confirm brain death, the discovery of Nu-complexes does not suggest that a patient who has been diagnosed with brain death will recover.

“The current criteria for diagnosing brain death are extremely stringent,” the study’s senior author Florin Amzica said in a statement. Rather than altering those criteria, Amzica noted that his team’s results pointed to the potential therapeutic utility of extreme deep comas. “An inactive brain coming out of a prolonged coma may be in worse shape than a brain that has had minimal activity,” he said, implying that deeper, drug-induced comas could be beneficial for some patients.

“The results offer us a better understanding of the residual activity of the brain under coma or anaesthetic,” Steven Laureys, who leads a Coma Science Group at Liège University Hospital in Belgium and was not involved in the study, told New Scientist. “I think this is something to be investigated further,” he added.

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