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Hemispheric Asymmetry of Visual Cortical Response by Means of Functional Transcranial Doppler

We assessed the visual evoked response and investigated side-to-side differences in mean blood flow velocities (MBFVs) by means of functional transcranial Doppler (fTCD) in 49 right-handed patients with severe internal carotid artery (ICA) stenosis and 30 healthy volunteers, simultaneously in both posterior cerebral arteries (PCAs) using 2 MHz probes, successively in the dark and during the white light stimulation. Statistically significant correlation was shown in healthy and in patients (between MBFV in right PCA in physiological conditions and MBFV in right PCA during the white light stimulation and in the dark. The correlation between MBVF in right PCA and contralateral left PCA was not statistically significant. The correlation between ipsilateral left PCA was significantly higher than the one with contralateral right PCA.There is a clear trend towards the lateralisation of the visual evoked response in the right PCA. Considering the presented results obtained in our study, we can conclude that there is a clear trend towards the lateralization of the visual evoked response in the right PCA, being highly consistent with results of the previous studies and showing a general dominance of the right occipital lobe in the visual process. The right occipital lobe is more responsive to visual stimuli in terms of functional activation than the left one, indicated by a consistently higher blood flow velocity response on the right. fTCD was able to assess hemispheric visual dominance not only in healthy individuals, but also in patients with severe carotid disease and thus compromised anterior cerebral circulation. Furthermore, velocity changes between sides as a measure of hemispheric perfusion lateralization could be an indicator of posterior collateral pathway. The demonstrated right-sided asymmetry in posterior cerebral circulation in patients with severe carotid disease could possibly be taken into consideration in further trials according to stroke risk or outcome.

stroke; visual cortical response; functional transcranial doppler; neurosonology

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