[Spectral EEG-characteristics of subcortical ischemic brain lesion--a case study]

Although the EEG-changes caused by ischemic stroke are well known, data of the literature are rather ambiguous. The EEG-findings recorded in a patient with a unilateral subcortical ischemic lesion are evaluated with special emphasis related to the effect of the dynamics caused by eye opening.

Data recorded from a patient (54 years old male with a completed stroke involving the frontal and parietal subcortical region in the left side) were compared to those of a control group (12 healthy age matched subjects). Absolute and relative frequency spectra, theta/beta quotients, the interaction index characterizing the effect of eyes opening and the symmetry index were calculated from the EEG recorded in eyes closed and eyes open conditions. Data of the patient were compared to those recorded in the control group on the basis of 95% confidence intervals.

Irrespective of the recording conditions the predominance of slow activity and the increase of theta/beta quotients were found in the absolute frequency spectra. The increase of beta and beta2 frequency bands following eye opening on the side of the lesion were found to be less obvious than that seen on the intact side and that observed in the control group. With respect to the interaction index related to the side differences caused by eye opening the change of the beta2 frequency band was found to be the most conspicuouS. The symmetry index underscored the predominance of slow (delta, theta, alpha1) frequencies on the lesion side, and that of the fast (beta1, beta2) frequencies on the intact side in both recording conditions.

Localized lesion of the white matter without cortical damage can cause the predominance of slow activity and decrease of the fast frequency bands on the side of the lesion which can be shown by the absolute frequency spectra and is revealed by the symmetry index. The lack of functional reactivity of the fast frequencies in the side of the lesion can clearly be seen in the change of relative spectra following eye opening and on the basis of the calculation of the interaction index reflecting the dynamics of side differences.