Shaping Motor Neural Functioning of Developmental Stuttering to Improve Fluency

Investigators will evaluate the effect of different tES protocols targeting motor associative regions (about 10 "consecutive" stimulation sessions, in different days; tES will be compared to sham stimulation), in association with "canonical" speech therapy. About 30 right-handed adults with idiopathic and persistent DS since childhood will be recruited (age 18-59 years; please see below for inlusion/exclusion criteria). Participants will be subdivided in three groups (in association to speech therapy): two groups will undergo transcranial random noise stimulation or transcranial direct current stimulation, while the third group will undergo sham (placebo) stimulation . Effects will be assessed by measuring stuttering severity (i.e. objective evaluation of stuttering), behavioral/cognitive scales (i.e. subjective evaluation of stuttering), as well as a series of neurophysiological indexes useful to evaluate brain functioning and connectivity (e.g. TMS\[transcranial magnetic stimulation\]-induced motor/evoked potentials and EEG brain activity). Evaluations will be realized before the start of the tES protocols, as well as at the end of the cycles. Follow-up evaluations (starting from about 6 weeks after completion of stimulation sessions) are also foreseen after the end of the treatments.