Abstract
Transcranial random noise stimulation (tRNS) is a recent neuromodulation protocol. The high-frequency band (hf-tRNS) has shown to be the most effective in enhancing neural excitability. The frequency band of hf-tRNS typically spans from 100 to 640 Hz. Here we asked whether both the lower and the higher half of the high-frequency band are needed for increasing neural excitability. Three frequency ranges (100–400 Hz, 400–700 Hz, 100–700 Hz) and Sham conditions were delivered for 10 minutes at an intensity of 1.5 mA over the primary motor cortex (M1). Single-pulse transcranial magnetic stimulation (TMS) was delivered over the same area at baseline, 0, 10, 20, 30, 45 and 60 minutes after stimulation, while motor evoked potentials (MEPs) were recorded to evaluate changes in cortical excitability. Only the full-band condition (100–700 Hz) was able to modulate excitability by enhancing MEPs at 10 and 20 minutes after stimulation: neither the higher nor the lower sub-range of the high-frequency band significantly modulated cortical excitability. These results show that the efficacy of tRNS is strictly related to the width of the selected frequency range.
Highlights
Transcranial random noise stimulation is a recent neuromodulation protocol
A one-way repeated measures ANOVA showed no significant differences in motor evoked potentials (MEPs) amplitudes between Stimulation conditions (Low-hf-Transcranial random noise stimulation (tRNS), High-hf-tRNS, Sham) at baseline in Experiment 1 (F2,10 = 0.74, p = 0.49), and a paired t-test showed no significant differences between Stimulation conditions (Whole-hf-tRNS, Sham) at baseline in Experiment 2 (t10 = 1.16, p = 0.27)
This implies that any differences between conditions arising from hf-tRNS could not be attributed to differences at baseline
Summary
Transcranial random noise stimulation (tRNS) is a recent neuromodulation protocol. The high-frequency band (hf-tRNS) has shown to be the most effective in enhancing neural excitability. The full-band condition (100–700 Hz) was able to modulate excitability by enhancing MEPs at 10 and 20 minutes after stimulation: neither the higher nor the lower sub-range of the high-frequency band significantly modulated cortical excitability. These results show that the efficacy of tRNS is strictly related to the width of the selected frequency range. Hf-tRNS has been successfully applied for reducing pain in multiple sclerosis[12] and for decreasing motor cortex excitability in Parkinson’s disease[13], as well as for reducing depressive symptoms[14] and improving negative symptoms in schizophrenia[15] Both lf-tRNS and hf-tRNS have shown promising results in reducing tinnitus intensity and distress[16,17,18]. Despite the proliferation of studies probing the effects of tRNS on cognitive functions, only a few studies have investigated its fundamental principles of functioning and the impact of the various stimulation parameters such as stimulation intensity, stimulation duration and frequency band
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