Transcranial Random Noise Stimulation Enhances Visual Learning In Healthy Adults.

Recent psychophysical studies have demonstrated that visuo-perceptual functions can improve over multiple training sessions, both in healthy adults (Sagi, 2011) and in hemianopic stroke patients (Das et al., 2014). To date, rehabilitative therapies for hemianopic patients have shown significant improvements only after many weeks of daily training. Recent studies using transcranial direct current stimulation (tDCS) have shown enhancement of visual performance in normal subjects. Notably, when current is applied in a random noise mode (tRNS), effects are seen earlier and are longer lasting. Here, we asked whether tDCS or tRNS can be used to boost visual perceptual learning of global direction discrimination, thus providing a proof-of-concept for the potential use of this approach in pathological populations. We tested 40 healthy, visually-intact subjects, aged 19-26 who were randomly assigned to 4 training groups: "anodal tDCS", high frequency "hf-tRNS", "sham" and "no-stimulation". All subjects were trained to discriminate the left or right global motion direction of random-dot stimuli for 10 days (one session/day). Before and after training, we measured the subjects' direction range and motion signal thresholds. Brain stimulation was delivered concurrently with the training task. For the active stimulation conditions, anodal tDCS was delivered over the occipital pole, while for hf-tRNS and sham, electrodes were positioned bilaterally over the left and right occipital poles. On average, all subjects improved over the two-weeks training period. However, the hf-tRNS group attained a direction range threshold of 162.88° (subtracting day10 from day1), while the "tDCS", "sham" and "no stimulation" subjects attained a threshold of 53.57°, 126.6° and 88°, respectively. Paired sampled t-tests indicated a significant effect of hf-tRNS on performance relative to the other groups (p = .03). These results indicate that hf-tRNS may be a more effective intervention to boost visual perceptual learning than tDCS or no stimulation during visual training. Meeting abstract presented at VSS 2015.