Shaping the brain with electricity. Modulating cortical excitability and plasticity with transcranial random noise stimulation.

The development of new technologies, such as non-invasive brain stimulation (NIBS) methods, has become a new frontier in cognitive neuroscience. Transcranial electrical stimulation (tES) has recently established its role as a promising tool for influencing brain functions, and even for enhancing cognitive, perceptual or motor performances, with potential benefits for pathological conditions. Interest has raised in transcranial random noise stimulation (tRNS), which consists in the application of alternating current over the cortex at random frequencies. This thesis concentrates on the investigation of tRNS as a technique to boost brain functioning and to promote plastic effects. In particular, the focus is to investigate the neural plasticity of the human brain using tRNS independently and combined with behavioural training. The first study concentrates on tRNS effect of the high-frequency band on primary motor cortex (M1) excitability. The results suggest that a wide range, compared to the reduced frequency bands, is required to induce a cortical excitability increase. The second study describes an innovative experimental protocol consisting of tRNS coupled with perceptual training aimed to improve visual function in patients with amblyopia. By combining eight sessions of hf-tRNS with a lateral masking training, a general improvement in contrast sensitivity has been obtained and tRNS has been shown useful to improve visual acuity compared to sham stimulation. The third study involved, in addition to tRNS, an exergame training (physical exercise combined with a videogame) chosen as a potential training tool for healthy young adults to improve the motor response speed and the response time when inhibition is required. The protocol consists of eight sessions of motor and cognitive training associated with the activation of the prefrontal cortex activation (PFC), the target area. Interestingly, the exergame training led to an improvement of simple reaction time, while the tRNS showed its efficacy in a higher demanding task, the Go/NoGo, with faster performance in go trials. This manuscript aims to contribute to the understanding of the mechanisms of action of tRNS in modulating neural excitability and boosting brain plasticity and offers new insights into the combined approach of tRNS and behavioural training. Future directions include creating well-calibrated protocols exploiting NIBS and behavioural training, in order to improve, compensate and recovery our abilities toward new perspective of treatment.