Abstract
There is evidence that high-frequency transcranial random noise stimulation (hf-tRNS) is effective in improving behavioural performance in several visual tasks. However, so far there has been limited research into the spatial and temporal characteristics of hf-tRNS-induced facilitatory effects. In the present study, electroencephalogram (EEG) was used to investigate the spatial and temporal dynamics of cortical activity modulated by offline hf-tRNS on performance on a motion direction discrimination task. We used EEG to measure the amplitude of motion-related VEPs over the parieto-occipital cortex, as well as oscillatory power spectral density (PSD) at rest. A time–frequency decomposition analysis was also performed to investigate the shift in event-related spectral perturbation (ERSP) in response to the motion stimuli between the pre- and post-stimulation period. The results showed that the accuracy of the motion direction discrimination task was not modulated by offline hf-tRNS. Although the motion task was able to elicit motion-dependent VEP components (P1, N2, and P2), none of them showed any significant change between pre- and post-stimulation. We also found a time-dependent increase of the PSD in alpha and beta bands regardless of the stimulation protocol. Finally, time–frequency analysis showed a modulation of ERSP power in the hf-tRNS condition for gamma activity when compared to pre-stimulation periods and Sham stimulation. Overall, these results show that offline hf-tRNS may induce moderate aftereffects in brain oscillatory activity.
Highlights
High-frequency transcranial random noise stimulation is a non-invasive brain stimulation technique which has been shown to improve the performance in a range of Communicated by Francesca Frassinetti.1 3 Vol.:(0123456789)Experimental Brain Research (2021) 239:2399–2418 mechanisms (Chaieb et al 2015, 2009; Pirulli et al 2013)
The results showed that high-frequency transcranial random noise stimulation (hf-tRNS) modulated the excitability of the motor cortex by enhancing motorevoked potentials (MEPs), but these effects depended on the duration, intensity, and frequency of the electric stimulation, and on the specific electrode montage (Chaieb et al 2011; Inukai et al 2016; Moliadze et al 2014; Moret et al 2019; Terney et al 2008)
These results showed that behavioural performance was not influenced by the offline hf-tRNS stimulation
Summary
High-frequency transcranial random noise stimulation (hftRNS) is a non-invasive brain stimulation technique which has been shown to improve the performance in a range of Communicated by Francesca Frassinetti.1 3 Vol.:(0123456789)Experimental Brain Research (2021) 239:2399–2418 mechanisms (Chaieb et al 2015, 2009; Pirulli et al 2013). Several studies have assessed the effects of hf-tRNS to induce medium- and long-term changes in corticospinal excitability These studies delivered the stimulation over the motor cortex and measured the modulation of motorevoked potentials (MEPs) induced by single-pulse transcranial magnetic stimulation (TMS) delivered at different time points after the electric stimulation. The results showed that hf-tRNS modulated the excitability of the motor cortex by enhancing MEPs, but these effects depended on the duration, intensity, and frequency of the electric stimulation, and on the specific electrode montage (Chaieb et al 2011; Inukai et al 2016; Moliadze et al 2014; Moret et al 2019; Terney et al 2008). Relatively few studies have investigated the physiological effects of hf-tRNS outside the motor system Recent studies, recording both EEG and TMS-induced phosphene excitability, showed that hf-tRNS can modulate sensory-related cortical activity (Herpich e 2018; Rufener et al 2017; Van Doren et al 2014). The results showed that hf-tRNS was able to increase the excitability of the visual cortex (i.e. lower phosphene thresholds), starting immediately after stimulation and lasting for up to 60 min
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