Now You Feel both: Galvanic Vestibular Stimulation Induces Lasting Improvements in the Rehabilitation of Chronic Tactile Extinction

Abstract

Tactile extinction is frequent, debilitating, and often persistent after brain damage. Currently, there is no treatment available for this disorder. In two previous case studies we showed an influence of galvanic vestibular stimulation (GVS) on tactile extinction. Here, we evaluated in further patients the immediate and lasting effects of GVS on tactile extinction. GVS is known to induce polarity-specific changes in cerebral excitability in the vestibular cortices and adjacent cortical areas. Tactile extinction was examined with the Quality Extinction Test (QET) where subjects have to discriminate six different tactile fabrics in bilateral, double simultaneous stimulations on their dorsum of hands with identical or different tactile fabrics. Twelve patients with stable left-sided tactile extinction after unilateral right-hemisphere lesions were divided into two groups. The GVS group (N = 6) performed the QET under six different experimental conditions (two Baselines, Sham-GVS, left-cathodal/right-anodal GVS, right-cathodal/left-anodal GVS, and a Follow-up test). The second group of patients with left-sided extinction (N = 6) performed the QET six times repetitively, but without receiving GVS (control group). Both right-cathodal/left-anodal as well as left-cathodal/right-anodal GVS (mean: 0.7 mA) improved tactile identification of identical and different stimuli in the experimental group. These results show a generic effect of GVS on tactile extinction, but not in a polarity-specific way. These observed effects persisted at follow-up. Sham-GVS had no significant effect on extinction. In the control group, no significant improvements were seen in the QET after the six measurements of the QET, thus ruling out test repetition effects. In conclusion, GVS improved bodily awareness permanently for the contralesional body side in patients with tactile extinction and thus offers a novel treatment option for these patients.

Vestibular contributions to a right-hemisphere network for bodily awareness: Combining galvanic vestibular stimulation and the “Rubber Hand Illusion”

“…studies confirm that this level of GVS activates the vestibular organs, without effects persisting beyond the period of stimulation (Fitzpatrick and Day, 2004). Further, behavioural changes have been reported with such low intensities GVS (Wilkinson et al, 2010;Kerkhoff et al, 2011;Schmidt et al, 2013aSchmidt et al, , 2013bFerrè et al, 2013bFerrè et al, , 2013c. Carbon rubber electrodes (area 10 cm 2 ) coated with electrode gel were placed binaurally over the mastoid processes and fixed in place with adhesive tape.…”

Effects of age, sex and arm on the precision of arm position sense—left-arm superiority in healthy right-handers

“…Previous studies found that left-sided visuospatial neglect after right-brain damage is functionally associated with impaired arm position judgments in the contralesional arm (Schmidt et al, 2013a) and also with problems in other body-related spatial tasks such as left tactile extinction (Schmidt et al, 2013b) or in identifying left human hands (Reinhart et al, 2012). This proprioceptive deficit can be temporarily restored by GVS (Schmidt et al, 2013a).…”

Vestibular modulation of spatial perception

“…Our planned contrasts thus reflect hypothesis about plausible ways that vestibular stimulation might influence spatial perception. Distinguishing generic and specific effects of an intervention is an established method in biosciences, and has been used previously for vestibular interventions (Schmidt et al, 2013). …”