• Alejandra Vasquez, Alejandra Malavera, Deniz Doruk, Leon Morales-Quezada, Sandra Carvalho, Jorge Leite, and Felipe Fregni.
• Spaulding Neuromodulation Center, Spaulding Rehabilitation Hospital, Harvard Medical School, Boston, MA, USA.
• Neuromodulation. 2016 Oct 1; 19 (7): 679-688.

ObjectiveTo explore the duration of tPCS after effects given different durations of stimulation on power and interhemispheric coherence of the EEG frequency bands. Our hypothesis was that longer tPCS duration would induce a differential effect on the EEG analysis and a longer duration of after effects on the EEG frequency bands.Materials And MethodsWe conducted a double blind, sham controlled study in which forty healthy subjects were randomized to receive a single session of either 10, 20, 30 min of active (2 mA, random frequency between 6 and 10 Hz, ear clip montage) or sham tPCS. EEG was recorded before and after the intervention to assess tPCS induced after effects.ResultsWe found that 10 and 20 min of active tPCS induced a significant increase in alpha (p = 0.004) and theta (p = 0.006) coherence in the frontal region as compared with the sham stimulation. No significant changes were found with 30 min of stimulation (p < 0.05). The Kaplan Meier analysis showed that 10 and 20 min of tPCS induced after effects that lasted 50 min.ConclusionsThese results evidence the nonlinear relationship between the stimulation duration and the tPCS after effects, suggesting the presence of homeostatic mechanisms.© 2016 International Neuromodulation Society.

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