Rapid effect of high-frequency tRNS over the parietal lobe during a temporal perceptual learning task.

INTRODUCTION: Transcranial random noise stimulation (tRNS) is a noninvasive neurostimulation technique in which random current levels applied to scalp electrodes elicit temporary changes in cortical excitability (Terney et al., 2008). This experiment explores modulatory effects of high-frequency tRNS on neural plasticity during a temporal perceptual learning task. We measured sensitivity to onset asynchronies (SOAs) during a temporal order judgment task as a function of both practice and active stimulation.

METHODS: Twenty-four subjects were randomly assigned to one of four conditions: hf-tRNS (up to 1000 Hz) over hMT+; hf-tRNS over parietal cortex; sham stimulation; and behavior only. Subjects undergoing active hf-tRNS were stimulated for 20 consecutive minutes concurrent with the task. Subjects viewed two discs flickering black and white for 1000 ms at 7.5 Hz. These discs were presented with onset asynchronies ranging from -66 ms (left disc first) to +66 ms (right disc first). During the flicker cycle, each disc was temporarily displayed as a Gabor for 133 ms (sp. frequency: 1.25 cycle/deg). Subjects judged whether the right or left disc appeared as a Gabor first. Feedback was provided for five out of six blocks.

RESULTS: SOA values across blocks were compared to determine sensitivity to the timing of Gabor onsets. As the experiment progressed, subjects exposed to parietal hf-tRNS were significantly better at correctly judging temporal order of the embedded Gabor discs at small onset asynchronies (F(3,20)=14.37; p = 0) as compared to all other conditions.

CONCLUSIONS: Our results show the quick effect that parietal tRNS has in improving perceptual sensitivity during tasks that require attention to temporal patterns. These results shows promising insight into the relationship between cortical stimulation and neural plasticity, leading the way to neurostimulation as a possible therapy for patients suffering from neurological attention disorders. Meeting abstract presented at VSS 2015.