Article

Sensory extinction is frequent and often persistent after brain damage. Previous
studies have shown the transient influence of sensory stimulation on tactile
extinction. In the present two case studies we investigated whether subliminal
galvanic vestibular stimulation (GVS) modulates tactile extinction. GVS induces
polarity-specific changes in cerebral excitability in the vestibular cortices and
adjacent cortical areas in the temporo-parietal cortex via polarization of the
vestibular nerves. Two patients (DL, CJ) with left-sided tactile extinction due
to chronic (5 vs. 6 (1/2) years lesion age) right-hemisphere lesions (right
fronto-parietal in DL, right frontal and discrete parietal in CJ) were examined.
Both showed normal tactile sensitivity to light touch and yielded 90-100% correct
identifications in unilateral tactile stimulations for both hands. In Baseline
investigations without GVS and Sham-GVS both showed stable left-sided tactile
extinction rates of 40-55% (DL) and 49-72% (CJ). In contrast, one session of
right-cathodal GVS (intensity: 0.6 mA, duration: 20 min) permanently improved
tactile identification of identical stimuli, while a second session with
left-cathodal GVS significantly reduced left-sided extinction rates for different
stimuli in DL. Patient CJ's left-sided tactile extinction was significantly
improved by left-cathodal GVS (0.5 mA, 20 min) for different stimuli, while
right-cathodal GVS induced a significant reduction for identical materials. In
contrast, Sham-stimulation was ineffective. Improvements remained stable for at
least 1 year (DL) resp. 3 weeks (CJ). Control experiments ruled out improvements
in tactile extinction merely by retesting. In conclusion, chronic tactile
extinction may be permanently improved by GVS in a polarity-specific way.
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Langue : ANGLAIS