Browsing by Subject "ALTERNATING-CURRENT STIMULATION"

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  • Räty, Silja; Borrmann, Carolin; Granata, Giuseppe; Cardenas-Morales, Lizbeth; Schoenfeld, Ariel; Sailer, Michael; Silvennoinen, Katri; Holopainen, Juha; De Rossi, Francesca; Antal, Andrea; Rossini, Paolo M.; Tatlisumak, Turgut; Sabel, Bernhard A. (2021)
    Background: Occipital strokes often cause permanent homonymous hemianopia leading to significant disability. In previous studies, non-invasive electrical brain stimulation (NIBS) has improved vision after optic nerve damage and in combination with training after stroke. Objective: We explored different NIBS modalities for rehabilitation of hemianopia after chronic stroke. Methods: In a randomized, double-blinded, sham-controlled, three-armed trial, altogether 56 patients with homonymous hemianopia were recruited. The three experiments were: i) repetitive transorbital alternating current stimulation (rtACS, n=8) vs. rtACS with prior cathodal transcranial direct current stimulation over the intact visual cortex (tDCS/rtACS, n=8) vs. sham (n = 8); ii) rtACS (n = 9) vs. sham (n = 9); and iii) tDCS of the visual cortex (n = 7) vs. sham (n = 7). Visual functions were evaluated before and after the intervention, and after eight weeks follow-up. The primary outcome was change in visual field assessed by high-resolution and standard perimetries. The individual modalities were compared within each experimental arm. Results: Primary outcomes in Experiments 1 and 2 were negative. Only significant between-group change was observed in Experiment 3, where tDCS increased visual field of the contralesional eye compared to sham. tDCS/rtACS improved dynamic vision, reading, and visual field of the contralesional eye, but was not superior to other groups. rtACS alone increased foveal sensitivity, but was otherwise ineffective. All trial-related procedures were tolerated well. Conclusions: This exploratory trial showed safety but no main effect of NIBS on vision restoration after stroke. However, tDCS and combined tDCS/rtACS induced improvements in visually guided performance that need to be confirmed in larger-sample trials.
  • Hyvärinen, Petteri; Choi, Dawoon; Demarchi, Gianpaolo; Aarnisalo, Antti A.; Weisz, Nathan (2018)
    Background: Previous studies have shown that transcranial electrical stimulation can be successfully applied during simultaneous MEG measurements. In particular, using beamforming they have established that changes of stimulus induced as well as evoked activity can be inspected during transcranial alternating current stimulation (tACS). Objective/Hypothesis: We studied tACS-mediated changes of the auditory steady-state response (ASSR), hypothesizing that-due to the putatively inhibitory role of alpha oscillations-these evoked responses would be diminished. Methods: We compared ASSRs in conditions with and without 12-Hz and 6.5-Hz sinusoidal 1.5 mA tACS, applied bilaterally over temporal areas. Source-level activity was estimated using a linearly constrained minimum variance beamformer and compared across tACS conditions using paired t-tests following a condition-internal normalization procedure. Conclusions: By separating the electrical and auditory stimulation to non-overlapping parts of the frequency spectrum, we were able to compare auditory-evoked steady-state activity across tACS conditions. We observed a significant decrease in normalized ASSR power in the 12-Hz tACS condition, illustrating that tACS could induce immediate changes in auditory evoked activity. This study sets a methodology to further interrogate the causal roles of oscillatory dynamics in auditory cortices, as well as suggests perspectives for employing tACS in clinical contexts. (C) 2018 Published by Elsevier B.V.