P 209. Transcranial random noise stimulation: A new approach to stimulating the brain

Abstract

Transcranial random noise stimulation (tRNS) is a neuromodulatory technique that involves the delivery of a bi-directional, randomly oscillating current. Introduction of a positive DC offset to the stimulation can produce a polarity-specific randomly oscillating current that produces effects similar to that of transcranial direct current stimulation (tDCS). It is thought that tRNS modulates cortical excitability by interfering with the ongoing neural oscillations in the cortex. In contrast to using a direct current, tRNS may avoid the homeostatic neural mechanisms associated with repeated stimulation sessions. This may be an advantage in clinical treatment protocols which seek to induce cumulative neuroplastic changes over multiple sessions. To date, there has only been one reported use of tRNS with a positive DC offset for the treatment of depression. Findings were promising, suggesting therapeutic potential for this form of stimulation ( Chan et al. (2012) ). The present study aimed to elucidate the clinical potential of tRNS with a positive offset by examining its effects on motor cortical excitability in healthy participants. We aimed to examine the effect of 2 mA tRNS + 1 milliamp (mA) offset for 10 min on cortical excitability by using single pulse transcranial magnetic stimulation (TMS). This was compared to four other transcranial electrical stimulation (tES) conditions as follows: 2 mA tRNS without an offset, 1 mA tDCS, 2 mA tDCS and sham stimulation. Fifteen healthy participants will be tested across five sessions in a within-subjects design. One form of tES was tested at each session, the order of which was randomised for each participant. tES was applied to the left motor cortex. Sets of 20 motor evoked potentials (MEPs) were elicited in the right first dorsal interosseus (FDI) muscle using single-pulse TMS before and up to 90 min after tES. Peak-to-peak amplitude of each MEP was measured. The mean amplitude of all responses after tES was calculated and normalised to the baseline amplitude for each subject. Results from the first 10 participants show mean ( sd ) post-tES normalised MEPs as follows: 2 mA tRNS + 1 mA offset, 1.44 (0.38); 2 mA tRNS, 1.01 (0.11); 1 mA tDCS, 1.24 (0.15); 2 mA tDCS, 1.30 (0.18) and sham, 1.06 (0.13). Results from all 15 participants will be subsequently presented. This is the first empirical study examining the effect of tRNS with an offset on cortical excitability. Preliminary results suggest that tRNS with an offset leads to an increase in cortical excitability similar to that produced by tDCS. Further, tRNS with an offset appears to be more effective than tRNS without an offset in producing changes in cortical excitability. KAH is supported by an Australian Post-Graduate Award and University of New South Wales Brain Sciences Top-Up Scholarship.