Brain Oscillatory Activity during Tactile Stimulation Correlates with Cortical Thickness of Intact Areas and Predicts Outcome in Comatose Patients

This study reports a correlation between EEG and structural brain changes in patients after severe traumatic brain injury in a coma. The novelty of our approach was based on the combination of structural visualization (MRI) and functional neuroimaging (EEG) during tactile stimulation. The structural morphometry indicated a decrease of whole-brain cortical thickness, the gray-matter volume of the cortex, and subcortical structures in comatose patients compared to healthy subjects. In resting-state EEG, coma patients had significantly higher power of the slow-wave activity of 2-6 Hz and significantly less power of the alpha and beta rhythm. Importantly, coma patients showed a significant decrease of theta-rhythm power in tactile stimulation compared to the resting state, and this EEG pattern was not found in the control group. The decrease of the theta-rhythm power significantly correlated with the better outcome from a coma. Spectral changes in EEG in response to tactile stimuli showed no association with brain morphometric measures in healthy controls. In patients, decreasing theta-rhythm power correlated positively with the volume of whole-brain gray matter, right putamen, and insula; and negatively with the volume of damaged brain tissue. Increasing beta-rhythm power, specific tactile EEG response for a healthy brain, correlated with the cortical thickness of the somatosensory Paracentral and Precentral area. The observed decrease of gray-matter volume indicates brain atrophy in coma patients, which could be associated with neurodegeneration induced by injury. Our results also demonstrate that slow-wave desynchronization, as a nonspecific response to tactile stimulation, can serve as a sensitive index of morphometric changes after brain injury and coma outcome.