Random noise stimulation improves neuroplasticity in perceptual learning

Abstract

Perceptual learning is considered a manifestation of neural plasticity in the human brain. We investigated brain plasticity mechanisms in a learning task using noninvasive transcranial electrical stimulation (tES). We hypothesized that different types of tES would have varying actions on the nervous system, which would result in different efficacies of neural plasticity modulation. Thus, the principal goal of the present study was to verify the possibility of inducing differential plasticity effects using two tES approaches [i.e., direct current stimulation (tDCS) and random noise stimulation (tRNS)] during the execution of a visual perceptual learning task.

Figure 1.

Trial structure. Example of an orientation discrimination task trial with the reference and target stimuli presented in the upper right hemifield.

Figure 2.

Experimental procedure. The main experiment was designed to be between subjects with six stimulation conditions: hf-tRNS, lf-tRNS, a-tDCS, c-tDCS, sham, and Cz. Subjects received the stimulation only in the first five blocks. The last block was a fictitious block (white represented); data from this block were not analyzed.

Figure 3.

Main experiment results. Data are represented as the mean ± SEM. The lines represent the fit of each condition: the broken line corresponds to hf-tRNS, the continuous thin line corresponds to lf-tRNS, the dotted line represents a-tDCS, the mixed dotted-broken line represents c-tDCS, the continuous thick line corresponds to sham, and the double gray line represents Cz stimulation. The asterisk near the curly bracket indicates the statistically significant differences between hf-tRNS and the conditions in the square bracket (p < 0.05).

Figure 4.

Control-hf-tRNS experiment results compared with main experiment hf-tRNS and sham groups. Data of control-hf-tRNS group are represented as the mean ± SEM. The lines represent the fit of each condition: the thick dashed line corresponds to control-hf-tRNS, the thin dashed line corresponds to hf-tRNS, and the continuous thick line corresponds to sham. The asterisk near the curly bracket indicates the statistically significant differences between both control-hf-tRNS and sham (p < 0.05) and hf-tRNS and sham (p < 0.05).