tACS increases alpha burst duration in a frequency- and montage-specific manner

Abstract

Transcranial alternating current stimulation (tACS) can experimentally manipulate neural oscillations in humans non-invasively. Previous studies consistently suggest that 10 Hz tACS in posterior regions leads to a general increase in alpha (7-15 Hz) oscillations. However, the specificity of this effect regarding stimulation frequency and location as well as its consequences on cognition are still unclear. We therefore aimed to investigate whether the putative effects of tACS on neural oscillations and cognition are specific to posterior stimulation in the alpha frequency range. We tested these effects using a 2 x 2 design (posterior or fronto-parietal stimulation, at 10 Hz or 6 Hz) plus a no-stimulation control group, during a sustained attention task.158 healthy participants were randomly allocated to control group (no stimulation) or one of the four active groups. All participants underwent an Electroencephalography recording and completed the Amsterdam Resting State Questionnaire before and after stimulation. Our results show that, relative to the control group, alpha power increases significantly after stimulation for the group receiving posterior 10 Hz stimulation and that this was explained by an increase in alpha oscillatory bursts duration rather than their amplitude. On the other hand, no significant differences were found between active and controls groups in behavioural performance or resting state cognition. Together, our findings demonstrate that tACS increases the duration of alpha oscillatory bursts in a montage- and frequency-specific manner and that this modulation is not accompanied by significant changes in sustained attention during stimulation or resting state cognition after stimulation.