An electroencephalogram (EEG) is a way to measure brain activity, a particularly useful indicator among those who have fallen into a coma. The deeper a person falls, the flatter the waveform gets, with a flatline conventionally thought to indicate brain death. But the discovery of an even deeper state of coma — one in which the brain is still active, even though the line is flat — calls this belief into question.
Dr. Bogdan Florea, a physician at Regina Maria Medical Center in Cluj-Napoca, Romania, discovered the possibility of a deeper state while observing a patient who had been put in a coma to control seizures induced from cardiac arrest. He noticed that although the patient’s brain activity flatlined, every few minutes there would be small infractions lasting just a few minutes, according to LiveScience.
“There’s a deeper form of coma that goes beyond the flat line, and during this state of very deep coma, cortical activity revives,” Florin Amzica, a neurophysiologist at Université de Montréal, told LiveScience.
Upon his discovery, Florea asked Amzica to research what might have happened. For their study, the researchers put cats under the same anesthetic drugs as the patient. The EEG flatlined, but an EEG only measure brain activity in the cortex, the outermost layer of tissue of the brain. However, signals from electrodes planted deeper within the brain showed that there were small bursts of activity coming from the hippocampus, and spreading throughout the brain.
“These ripples build up a synchrony that rises in a crescendo to reach a threshold where they can spread beyond the hippocampus and trigger activity in the cortex,” Amzica told NewScientist.
One possible explanation for this phenomenon, Amzica said, is that other parts of the brain could have lost their control over the hippocampus, which is responsible for learning and memory, as the brain fell into a coma. Therefore, the hippocampus could become active without being disturbed by the other parts of the brain.
While the discovery may not help comatose patients with severe brain damage, it could offer benefits to those who have experienced physical trauma, drug overdoses, or life-threatening seizures, since inducing a comatose state could help protect their brains from further damage.
Source: Amzica F, Florea B, Kroeger D. Human Brain Activity Patterns beyond the Isoelectric Line of Extreme Deep Coma. PLOS One. 2013.