Reduced intracortical inhibition and facilitation in the primary motor tongue representation of adults who stutter

Objective: We aimed at detecting neurophysiological changes, in the primary motor tongue representation in adults with persistent stuttering. Methods: Using transcranial magnetic stimulation in 12 patients and 14 controls, we examined motor threshold, motor-evoked potential (MEP) input-output curve, short-term intracortical inhibition (SICI) and intracortical facilitation (ICF), based on eight trials per conditioning-test interval. Results: In controls inhibition of the MEP-amplitude at short inter-stimulus intervals (ISI) and facilitation of the MEP-amplitude at long ISIs was evident. Patients showed an inhibition at ISI 3 ms and weaker nonsignificant inhibition at ISI 2 ms; this delay of inhibitory activity was especially prominent in the right hemisphere. Facilitation was reduced at ISI 10 and 15 ms in patients. Furthermore, MEP input-output curve was steeper in patients. Motor thresholds did not differ between groups. Conclusions: In persistent stuttering intracortical excitability of the primary motor tongue representation is altered with a deviant time course for inhibitory activity in the right hemisphere and reduced paired-pulse facilitation. Significance: These results specify changes in intracortical networks possibly mediated by altered GABAergic regulations in persistent stuttering. Thus, a better understanding of pathomechanisms and a potential role in understanding pharmacological treatment responses emerge by using transcranial magnetic stimulation. (C) 2011 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.