S152. Modulation of motion perception by bilateral MT/V5 tDCS stimulation

Abstract

Introduction Transcranial direct current stimulation (tDCS) is able to modulate the cortical excitability underneath the stimulating electrode, hence altering its function. Previous studies have demonstrated that tDCS over middle temporal visual area (MT/V5), with the reference electrode over the frontal or central cortex, was able to interfere the correct answer rate to random dot motion (RDM) test. Nevertheless, whether the effect came from the active electrode (i.e. over unilateral MT/V5) or the reference electrode remained elusive. In this study, we applied tDCS stimulation, either anodal or cathodal, over bilateral MT/V5, with referenced to a common extra-cranial electrode over chin, to further elucidate if the effect is derived from MT/V5 modulation. Methods Fifteen subjects (M/F: 6/9, mean age: 30.0 ± 9.4 years) participated in this study. Before tDCS treatment, a baseline simple random dot motion test (sRDM) was performed. Subjects were seated comfortably in a semidarkened room at a distance of 75 cm from the monitor. A forced-choice motion-direction discrimination task was used. Subjects had to report the direction (left or right) of the coherent motion dots presenting in the center of the monitor, in a 10 o × 10 o window. After a learning session that all subjects were able to answer correctly approximately 75%, 50 trials were tested to calculate the accurate rate. Bilateral MT/V5 tDCS stimulation, either anodal or cathodal, was then applied, with the reference electrode placed over chin. The current was applied for 20 min with an intensity of 2.0 mA. After tDCS treatment, the sRDM was repeated for 3 times (10 min apart each other). Results After anodal tDCS treatment, a transient improved accuracy of sRDM was observed. The accuracy changed from 0.77 ± 0.11 (pre) to 0.81 ± 0.11 (post_1), 0.78 ± 0.12 (post_2), 0.72 ± 0.13 (post_3), p = 0.019, Friedman test. Post-hoc Wilcoxon signed-rank test showed that the difference came from pre vs. post_1 (p = 0.042), post_1 vs. post_3 (p = 0.027), and post_2 vs. post_3 (p = 0.042). Alteration of sRDM accuracy was not observed after bilateral MT/V5 cathodal tDCS stimulation. Conclusion Bilateral MT/V5 anodal tDCS stimulation is able to modulate the function in motion perception. Our study provided evidence that tDCS may exert its modulatory effects through MT/V5 directly.