Therapeutic Effects of Transcranial Alternative Current Stimulation (tACS) in Chronic Post Stroke Hemianopia

Detailed Summary

Background: The most common visual field deficit after retro-chiasmatic lesions is homonymous hemianopia (HH), defined as the impossibility of seeing the contralesional visual hemisphere without ocular injury. HH affects between 90000 and 120 000 new cases per year in the United States and Europe HH was reported in 30% of patients after stroke (National Audit Office) (in France, with 130,000 strokes per year, 39,000 patients with HH). Despite the 30-year decline, the rehabilitation techniques have a low level of evidence of their effectiveness and few are used in routine clinical practice in France. Transcranial Alternate Current Stimulation (tACS) is a method of Alternative Current stimulation that can modulate neural activity by imposing local oscillatory activity. An observational study of occipital tACS in patients with optic nerve lesions showed an increase in visual field size, power, and occipital alpha synchrony. Two transorbital tACS studies showed visual improvements , and compensations for abnormally weak oscillatory activity by temporal resynchronization. Our team has demonstrated a role of noninvasive brain stimulation in right hemisphere frontal eye fields on cortical beta-high (\~ 30 Hz) oscillatory activity, improving the visual perception of both hemi-fields and the fronto-parietal synchrony of the right hemisphere. Objective: This project aims to compare, on the same patient population, two tACS stimulation strategies, with the aim of increasing the attentional orientation towards the blind visual hemi-field and thus the visual detection of stimuli in this hemi-field. . For this, The investigator team will evaluate on the one hand an occipital stimulation (V1-IPS) contralateral to the lesion, at a alfa frequency (10 Hz), which induces the desynchronization of the contralateral hemisphere with the aim of improving the visual perception of targets in the blind visual hemi-field. the study will compare this intervention to a stimulation of the frontal region (FEF) of the right hemisphere at a high-beta frequency (30 Hz), which showed effects of facilitation of endogenous and exogenous attentional orientation. The two previous strategies will be compared to a placebo tACS stimulation session.

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