Objective: 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 sub-cortical 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 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.
Horizontal T1 weighted MRI images demonstrate marked asymmetry of damage to subcortical structures. Note loss of right thalamus and basal ganglia structures, and left posterior thalamic injury.
Spectral power and coherence over frequency bands. Delta 1 to 4 Hz, theta 4 to 8 Hz, alpha 8 to 13 Hz, beta 13 to 30 Hz, gamma 30 to 50 Hz. F Frontal, C Central, P Parieto-temporal.