Topographic EEG analysis in two patients with basilar thrombosis.

The EEG activity of two patients with occlusion of the vertebral and basilar arteries was analyzed. Power maps, peak power frequency, and field power differences during both photic drive and verbal command were evaluated. Clinical findings of one patient fit the criteria of locked-in syndrome. Photic stimulation and event related desynchronization paradigm was used for testing the reactivity of EEG. Averaged EEG epochs during intended movement after verbal command showed significant alpha and sub-alpha power reduction. Regional differences of EEG reactivity were assumed secondary to the underlying hemispheric infarcts. Awareness of the patient in a locked-in state was documented by EEG analysis. In the second case permanent vegetative state was associated with a nonreactive rhythmic alpha pattern. Time sequence analysis of power ratios showed spontaneous alternating activity of alpha and sub-alpha generators. The authors conclude that pseudo-periodic fluctuation of alpha activity reflects partial preservation of thalamo-cortical connections.