The tolerability of transcranial electrical stimulation used across extended periods in a naturalistic context by healthy individuals.

Transcranial electrical stimulation (tES) is one of the most widely implemented forms of non-invasive neuromodulation in basic and clinical neuroscience. Further, the use of tES by healthy populations for various purposes is growing widespread daily. The effects of tES protocols on the skin and other tissues has remained uncharacterized when used across extended periods of time by healthy individuals. Therefore, we examined the basic safety and tolerability profile of two distinct tES protocols used repeatedly across an extended period of time by healthy subjects and report our findings here for the first time. The safety and tolerability profile previously accumulated regarding extended use of tES in clinical populations is compelling and supports a low-risk or non-significant risk designation. In the present study, we tested the tolerability (safety) and compliance, compared to sham, of two common tES approaches having a current density < 2 mA/cm2; transcranial Direct Current Stimulation (tDCS) or transcranial Pulsed Current Stimulation (tPCS) used by healthy subjects three to five days (17- 20 minutes per day) per week for up to six weeks in a naturalistic environment. In this study 100 health