Modulating fluency with Transcranial Magnetic Stimulation over right or left inferior frontal gyrus

Abstract

Objective In these last years, a growing body of evidence has already indicated that non-invasive brain stimulation techniques, such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), can modulate the language system in aphasic populations. The aim of this presentation is to investigate for the first time the effects of inhibitory rTMS over the left and right inferior frontal gyrus (IFG) on phonemic fluency tasks. Participants Sixty-six right-handed healthy participants participated in the study. Forty-four had administered offline low-frequency (1 Hz) rTMS for 10 minutes and verbal fluency outcome measures were recorded. Twenty-two participants were assigned to the control group, with only measures of verbal fluency recorded, to evaluate the potential contribution of practice effects on verbal fluency tasks. Results rTMS-inhibition of the right IFG improved verbal fluency performance while rTMS-inhibition of the left IFG worsened fluency performance. There is no evidence that the results were the subject of practice effects. Conclusion These findings suggest that the cerebral network dedicated to verbal fluency processing is facilitated by inhibitory rTMS over the right IFG. We hypothesize that, in healthy participants, the application of inhibitory rTMS over the right IFG may decrease the interhemispheric inhibition to the left frontal regions critical for verbal fluency and improve verbal fluency performance. We suggest that a similar stimulation protocol may be used to enhance phonemic fluency performance in left frontal patients affected by oral language production deficits.