Cerebellar Transcranial Direct Current Stimulation Effects on Saccade Adaptation

Figure 1

Experimental paradigms, single subject data, and population data. Panel (a) depicts inward adaptation where subjects performed an inward paradigm that consisted of 50 baseline trials of 20° saccades at intervals between 1.5 and 2 s, followed by 150 adaptation trials where the second target had an intrasaccadic step of 5°. Eye trace shows an overshoot at the beginning of the phase and the subject makes a corrective saccade to the target. Finally, 50 postadaptation trials presented in the same way as baseline trials. Anodal tDCS was delivered for 15 min at the start of the experiment or for 30 s in the sham condition. Panel (b) shows outward adaptation consisting in the same trial structure as inward, but here the subjects experienced baseline trials of 15° saccades and a forward jump of 5° (in the direction of the saccade). The middle row shows examples of adaptation for a single subject in the inward adaptation (gain-decrease, panel (c)) and outward adaptation (gain-increase, panel (d)) experiment for the two tDCS conditions. Lines on the top depict blocks composed of the median values of 10 trials. The bottom row shows group data for inward (panel (e)) and outward (panel (f)) adaptation. Thin, low-opacity lines show the course of adaptation for all subjects. Thick lines on the top show the median value for all of the subjects for both paradigms in the two stimulation conditions. For the inward adaptation experiment no differences were observed in baseline or postadaptation phases but presented a significantly smaller gain under cerebellar tDCS condition (). In the outward adaptation experiment, subjects also presented a normal course of adaptation in which subjects in the sham condition present relatively smaller gains compared to tDCS condition observed since the baseline phase, though this was not significant in any of the three phases (see Section 3). Gray bars show the measures taken into account for the analysis in this study. (atDCS: anodal transcranial direct current stimulation. Post-A: postadaptation. Blue: sham, red: tDCS.)

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