What do you feel if I apply transcranial electric stimulation? Safety, sensations and secondary induced effects.
OBJECTIVE
The goals of this work are to report data regarding a large number of stimulation sessions and to use model analyses to explain the similarities or differences in the sensations induced by different parameters of tES application.


METHODS
We analysed sensation data relative to 693 different tES sessions. In particular, we studied the effects on sensations induced by different types of current, categories of polarity and frequency, different timing, levels of current density and intensity, different electrode sizes and different electrode locations (areas).


RESULTS
The application of random or fixed alternating current stimulation (i.e., tRNS and tACS) over the scalp induced less sensation compared with transcranial direct current stimulation (tDCS), regardless of the application parameters. Moreover, anodal tDCS induced more annoyance in comparison to other tES. Additionally, larger electrodes induced stronger sensations compared with smaller electrodes, and higher intensities were more strongly perceived. Timing of stimulation, montage and current density did not influence sensations perception. The analyses demonstrated that the induced sensations could be clustered on the basis of the type of somatosensory system activated. Finally and most important no adverse events were reported.


CONCLUSIONS
Induced sensations are modulated by electrode size and intensity and mainly pertain to the cutaneous receptor activity of the somatosensory system. Moreover, the procedure currently used to perform placebo stimulation may not be totally effective when compared with anodal tDCS.


CONCLUSIONS
The reported observations enrich the literature regarding the safety aspects of tES, confirming that it is a painless and safe technique.
Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy. Electronic address: anna.fertonani@cognitiveneuroscience.it.
Anna
A
Fertonani
Statistics Service, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy.
Clarissa
C
Ferrari
Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy; Neuroscience Section, Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy. Electronic address: carlo.miniussi@cognitiveneuroscience.it.
Carlo
C
Miniussi
D000328:Adult; D000367:Age Factors; D000368:Aged; D004566:Electrodes; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012449:Safety; D012677:Sensation / Q000502:physiology*; D012867:Skin / Q000294:innervation; D011795:Surveys and Questionnaires; D065908:Transcranial Direct Current Stimulation / Q000009:adverse effects*
Questionnaire; Sensations; Transcranial alternating current stimulation (tACS); Transcranial direct current stimulation (tDCS); Transcranial random noise stimulation (tRNS); tES