Background: Recent studies show conscious perception is correlated with firing rate synchronization across multiple neuronal assemblies. This study explores the synchrony between multiple cortical surface sites as brain injury patients emerge from coma.
Methods: Scalp electrode EEG recordings were collected and analyzed from 13 traumatic brain injury patients during their stay in a neurosurgical intensive care unit. Neuronal synchrony was calculated between various electrode pairs during comatose and conscious periods defined by the GCS. Frequency bands from 1 to 30 Hz were evaluated in each patient.
Results: As patients emerged from coma at GCS 3 to GCS scores > or =8, synchrony values from all electrode pairs revealed a global decrease in synchrony at higher GCS scores. No significant effects were detected relative to the amount of sedation given, but at higher GCS scores significantly increased neuronal synchrony was observed between occipital lobes and right parietal and temporal lobe sites. Synchrony was decreased between frontal-occipital, frontal-parietal, and parietal-occipital electrodes.
Conclusions: In frequencies from 1 to 30 Hz, synchrony between right parietal and temporal lobes, as well as bilateral occipital lobes, tends to be increased as patients emerge from comatose states. However, synchrony between most intrahemispheric cortical sites is decreased at higher GCS scores in most of the above frequency bands. Thus, brain injury patients demonstrate both increased and decreased cortical surface synchrony between different lobes during emergence from coma.