Optimal random frequency range in transcranial pulsed current stimulation indexed by quantitative electroencephalography

Given the recent results provided by previous investigations on transcranial pulsed current stimulation (tPCS) demonstrating its modulatory effects on cortical connectivity; we aimed to explore the application of different random pulsed frequencies. The utility of tPCS as a neuromodulatory technique for cognition performance will come as additional frequency ranges are tested with the purpose to find optimal operational parameters for tPCS. This study was designed to analyze the effects of tPCS using the following random frequencies; 1-5, 6-10, and 11-15Hz compared with sham on quantitative electroencephalographic changes in the spectral power and interhemispheric coherence of each electroencephalographic frequency band. This was a parallel, randomized, double-blinded, sham-controlled trial. Forty healthy individuals older than 18 years were eligible to participate. The main outcomes were differences in the spectral power analysis and interhemispheric coherence as measured by quantitative electroencephalography. Participants were randomly allocated to four groups of random frequency stimulation and received a single session of stimulation for 20min with a current intensity of 2mA delivered by bilateral periauricular electrode clips. We found that a random pulsed frequency between 6-10Hz significantly increased the power and coherence in frontal and central areas for the alpha band compared with sham stimulation, while 11-15Hz tPCS decreased the power for the alpha and theta bandwidth. Our findings corroborate the hypothesis that a random frequency ranging into the boundaries of 6-10Hz induces changes in the naturally occurring alpha oscillatory activity, providing additional data for further studies with tPCS.