Power spectra and coherence in the EEG of a vegetative patient with severe asymmetric brain damage.

OBJECTIVES To examine differences in power spectra and intra-hemispheric coherence between the left and right hemispheres in the presence of severe asymmetric brain damage. METHODS Power spectra and coherence functions were computed for a patient with severe damage to subcortical gray matter structures on the right side but relative preservation on the left. RESULTS Power spectra differed modestly over the hemispheres, with greater low frequency power and less high frequency power over the more damaged right hemisphere. Coherence differed dramatically, with marked reduced coherence over the right hemisphere, particularly frontally where the damage was most extensive. CONCLUSIONS Damage to subcortical structures of one hemisphere may result in a marked reduction in coherence in the ipsilateral EEG with only a modest change in the power spectrum. We speculate that the physiologic basis of this selective change is damage to structures mediating communication between cortical areas.