Do somatosensory oscillations relate to tactile attention? Extracting the phase of transcranial Alternating Current Stimulation (tACS) during stimulus presentation.

Attentional mechanisms allow for the prioritization of information depending on the task at hand. Evidence from Electroencephalography (EEG) suggests that lateralised changes in the amplitude of alpha oscillations (8-­‐14 Hz) are linked to orienting attention and that the phase of an oscillatory cycle can affect how behavioral and perceptual information is processed. Transcranial alternating current stimulation (tACS) is a non-­‐invasive brain stimulation method that involves the application of weak electric currents to the scalp. tACS provides the ability to entrain intrinsic oscillations to specific frequencies. Through the employment of new hardware, the timings of stimuli presentation and the phase of tACS signals were accurately recorded so that their timings could be compared. This setup was implemented in an ongoing study that utilised participant individualized alpha and beta (25 Hz) stimulation during two tactile attention tasks. Results indicated that during alpha stimulation, performance in an endogenous tactile attention was mediated by the phase of the tACS signal, with a distribution of reaction times (RTs) that approximately followed the pattern of the waveform signal. The phase of the tACS signal during beta stimulation was shown to mediate performance during an exogenous tactile attention task. Both these results indicate that the fastest and slowest RTs occur at opposite phase positions of the tACS signal, providing novel evidence for a phasic relationship between performance variability and somatosensory attention.