Tes and its Effects on Cognitive FUnctions: Feasibility and Limitations for a Broader Clinical Application

Trascranial electrical stimulation (tES) is a neuromodulation technique which applies a mild current to modulate a wide variety of cognitive functions. It was shown that depending on the protocol applied, tES is effective in enhancing or interfering with cortical excitation, even if further research is needed in order to better understand its effects. In our studies, we focused on the online or offline effects of various tES protocols and on disparate tasks, in order to evaluate potential future application on clinical population. To date, few studies investigated offline, transfer effects of tES, both after single or multiple sessions administration. Similarly, evidence assessing tES offline and long-term effects on cortical excitability is still lacking. This doctoral thesis contributed to shed light on different aspects concerning tES. Firstly, we demonstrated that cathodal tDCS applied over right inferior frontal gyrus (rIFG) is effective in modulating selectively incongruent trials in a dots comparison task. Moreover, the effect was specific for offline measures, but not online, suggesting possible short-term after-effects of this protocol. Secondly, we showed that bilateral tRNS is more effective than anodal tDCS in inducing after-stimulation changes in attention both on behavioral performance and cortical excitation. Our studies confirmed that the two protocols are differentially effective, consistently with literature showing that different neural mechanisms underlie tDCS and tRNS neural after-effects. Finally, we demonstrated that despite the absence of online effects, coupling bilateral tRNS with cognitive training is effective to induce long-term changes, as assessed by behavioral measures and cortical plasticity investigations. Interestingly, the effects were still present a month after the end of the training. Taken together, our studies contributed to better understand the after-effects of tES and suggests that bilateral tRNS is best suited for clinical applications, even if further research is needed.