Abstract
Transcranial direct current stimulation (tDCS) is proposed as a tool to investigate cognitive functioning in healthy people and as a treatment for various neuropathological disorders. However, the underlying cortical mechanisms remain poorly understood. We aim to investigate whether resting-state electroencephalography (EEG) can be used to monitor the effects of tDCS on cortical activity. To this end we tested whether the spectral content of ongoing EEG activity is significantly different after a single session of active tDCS compared to sham stimulation. Twenty participants were tested in a sham-controlled, randomized, crossover design. Resting-state EEG was acquired before, during and after active tDCS to the left dorsolateral prefrontal cortex (15 min of 2 mA tDCS) and sham stimulation. Electrodes with a diameter of 3.14 cm2 were used for EEG and tDCS. Partial least squares (PLS) analysis was used to examine differences in power spectral density (PSD) and the EEG mean frequency to quantify the slowing of EEG activity after stimulation. PLS revealed a significant increase in spectral power at frequencies below 15 Hz and a decrease at frequencies above 15 Hz after active tDCS (P = 0.001). The EEG mean frequency was significantly reduced after both active tDCS (P < 0.0005) and sham tDCS (P = 0.001), though the decrease in mean frequency was smaller after sham tDCS than after active tDCS (P = 0.073). Anodal tDCS of the left DLPFC using a high current density bi-frontal electrode montage resulted in general slowing of resting-state EEG. The similar findings observed following sham stimulation question whether the standard sham protocol is an appropriate control condition for tDCS.
Highlights
Transcranial direct current stimulation is a non-invasive brain stimulation technique used to explore cognitive functioning across a wide range of domains (Coffman et al, 2014)
In 8 of the 18 participants the EEG amplitude increased dramatically for the duration of Transcranial direct current stimulation (tDCS), whereas in the other participants the increase in amplitude was mainly confined to the beginning and end of stimulation
The corresponding power spectral density (PSD) revealed a broad increase in spectral power across all frequencies, the largest increase was observed at frequencies below 5 Hz
Summary
Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique used to explore cognitive functioning across a wide range of domains (Coffman et al, 2014). Therapeutic potential has been reported in neuropathological disorders including depression (Arul-Anandam and Loo, 2009; Nitsche et al, 2009; Loo et al, 2010, 2012; Brunoni et al, 2013), Slowing of EEG after tDCS stroke (Boggio et al, 2007; Baker et al, 2010), and dementia (Kuo et al, 2014). Complex interactions of stimulation polarity, direction of electric current (i.e., radial or perpendicular to neuronal axes), and baseline levels of neuronal activity determine whether tDCS effects will be excitatory or inhibitory (Nitsche and Paulus, 2000; Jacobson et al, 2012b; Bikson and Rahman, 2013; Rahman et al, 2013). The after-effects of tDCS can last for an hour or longer following as little as 5 min of stimulation (Nitsche and Paulus, 2000)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
