The longer a patient remains in a coma following a traumatic brain injury (TBI), the less likely they are to regain consciousness. But researchers have now found a biomarker on electroencephalograms (EEG) that may help doctors predict if patients have the potential to recover consciousness, even years after injury.

Loss of consciousness is not uncommon after a traumatic brain injury, and it is usually short-lived. A minority of patients, however, go on to develop disorders of consciousness (DOCs), which can become permanent.

The problem is that, on the surface, these patients can look exactly alike. Having a better idea if someone had the potential for recovery could have huge implications on treatment, rehabilitation, and long-term care.

A team of researchers out of the University of Birmingham in the United Kingdom performed a meta-analysis of resting-state EEGs on patients who had lost consciousness following TBI. Their results were published in December 2020 in Frontiers in Neurology.

Most of the research analyzed in their study was done on patients with shorter-term loss of consciousness (less than a year) after brain injury. But a few studies were included in the meta-analysis that focused on longer term patients. What these studies had in common was an association between regaining consciousness and higher measures of alpha power (8–13Hz).

This correlation suggests ongoing monitoring is important even after many DOCs could be considered permanent, according to the study.

Alpha waves are produced in the thalamus, and higher alpha power indicates that thalamocortical loops are functioning. Intact thalamocortical loops are a prerequisite for consciousness. Therefore, even in an unconscious patient, if these loops are not mechanically or functionally inhibited, recovery of consciousness is possible.

This hypothesis is backed up by other studies showing that damage to the thalamus is common in DOCs. Further, consciousness has been shown to improve with stimulation of the thalamus.

“Based on the existing literature,” the authors wrote, “we suggest that resting-state EEG is particularly promising within the first year post-TBI, and that alpha power and variability are key measures for predicting functional outcome in this time period.”

Resting-state EEG offers distinct advantages in the assessment of unconscious patients, the authors point out. It can be done at the bedside, is cheaper and more convenient than other forms of brain monitoring, and patients don’t need to be actively involved in the testing.

“Given the growing evidence for late recovery after TBI, research into prognosis in [chronic disorders of consciousness], especially after the first year post-TBI, is a priority,” the authors conclude.