Most think of a coma as a state of limbo between life and death. The word “coma” conjures up an image of a seemingly lifeless patient, hooked up to a variety of monitoring devices. The most recognizable of these devices is the EEG. The EEG — or electroencephalogram — measures the brain activity of the patient.
Medical professionals have long accepted that a flat line EEG indicates an irreversible coma, one of the most serious types of comas. Furthermore, a flat line EEG is often an indication that the brain is no longer alive. However, new evidence may refute that belief.
“We discovered that a brain can survive during the flat EEG and can even be plunged in a deeper coma during which EEG activity is revived,” Florin Amzica, leader of the research team at the University of Montreal, said.
The accepted medical definition of a coma states that patients in a coma are in a state of unconsciousness and cannot respond to normal stimuli. Normal reflexes such as the avoidance of pain-causing stimuli are not producible under this stage. Comas are further classified into different types including alpha, hepatic, irreversible and myxedema comas. In some types of comas, brain activity is still measurable; notably, in alpha comas, the EEG registers alpha-wave activities within the brain. However, in irreversible comas, there is a flat line EEG, suggesting a lack of any brain activity.
In a recent study conducted by a team led by Amzica, researchers found evidence that there are still some traces of cerebral activity in irreversible coma patients. In the experiment, cats were placed in a deep coma using isoflurane, which is a common anesthetic. The cats were then subjected to an EEG exam, which ensured that all cats have a flat EEG reading. The researchers noted that all cats registered negative for activity in the cortex.
However, as the team observed activities in the hippocampus, the EEG registered activities within that region. The active hippocampus generated oscillations that were transmitted to the cortex. The evidence suggests that despite a flat line EEG, cerebral activities are still possible in regions of the brain other than the cortex. Furthermore, the researchers suggests that the EEG waves from the hippocampus may be analogous to those of humans.
The data gathered from the experiment leads to several conclusions. First, the research team determined that even when diagnosed with a flat line EEG, the brain is still capable of cerebral activities. A flat line EEG indicates a lack of cortex activity rather than the lack of brain activity.
In addition, the discovery of Nu-complexes points to the ability of the hippocampus to send information to a non-responsive cortex. The researchers propose that the activities from the hippocampus may be a self-protection system. Similar to the way an unused muscle atrophies, the brain may suffer more damage by remaining inactive. As a result, the hippocampus may send signals to the cortex in order to maintain a minimum activity level, reducing the atrophy that might occur under a long coma.
“It may result rather useful to keep a comatose brain in this state than in the lighter version of the isoelectric line, because the Nu-complex state generates cortical activities that might prevent synapses from degenerating as is probably the case during the flat line,” Amzica said.
The discovery of Nu-complexes can also indicate a more accurate form of measure for coma recovery.
“In this case, the triggering of Nu-complexes would testify in favor of a functional brain, with chances of return from coma, while absence of Nu-complexes would prove irremediable lost neuronal elements with no chance of recovery,”