Electroencephalographic coherence analysis in multiple sclerosis: Correlation with clinical, neuropsychological, and MRI findings

Objective - To explore functional corticocortical connections in multiple sclerosis by means of coherence of the EEG, and to evaluate their correlations with the degree of cognitive impairment and with brain lesion load assessed by MRT. Methods - EEG coherence was studied from 28 patients with clinically definite multiple sclerosis. Ten minutes of resting EEG were recorded with 20 scalp electrodes, with binaural reference. FFT power and coherence were calculated in artifact free epochs of 1 second and compared with values from 22 control subjects of comparable age and sex distribution. Patients also underwent MRI (n = 27) and neuropsychological examination (n = 21). Results - Compared with controls, patients with multiple sclerosis showed increased θ power in the frontotemporal-central regions (p <0.005). θ Band coherence was decreased between homologous areas (p <0.02). α Band coherence was decreased both in the local and long distance connections (p <0.0005). These findings were most striking both in patients with high MRI subcortical lesion load and in patients with cognitive involvement. A significant correlation was found between interhemispheric θ (p = 0.02) and α (p = 0.017) and anteroposterior α (p = 0.013) coherence and subcortical MRI lesion load, but not with exclusively periventricular lesion load. Conclusions - These findings support the hypothesis that cognitive impairment in multiple sclerosis is mostly dependent on involvement of corticocortical connections related to demyelination and/or axonal loss within the white matter immediately underlying the cortex.