The role of right inferior frontal gyrus in impulsivity: Insights from high-frequency repetitive transcranial magnetic stimulation

Abstract

It has been argued that right inferior frontal gyrus (rIFG) play a crucial role in impulsivity, particularly the response inhibition subdomain, through the findings from studies of low-frequency repetitive transcranial magnetic stimulation (rTMS). However, little attention has been paid to the effects of applying high-frequency (HF-rTMS) to rIFG on response inhibition and reflection impulsivity. Therefore, much uncertainty still exists about the feasibility of HF-rTMS on rIFG for clinical implications of improving impulse control. This study aimed to investigate the effects of applying HF-rTMS to rIFG on response inhibition and reflection impulsivity using two neurocognitive tasks. The association between self-reported and performance-based impulsivity was also examined to ascertain the poor to non-existent correlation found in previous studies. HF-rTMS (10Hz, 15 trains of 2 secs, 900 pulses in total with 100% resting motor threshold) was applied onrIFG to 20 healthy male adults in a randomised crossover sham-controlled study. Participants received both rTMS and shamstimulation on separate days and the Stop Signal Task (SST) and Information Sampling Task (IST) were used to assess responseinhibition and reflection impulsivity respectively. They also assessed their self-reported impulsivity with Barratt Impulsivity Scale -11 (BIS-11) and UPPS-P Impulsive Behaviour Scale (UPPS-P) Results indicated that participants did not show any significant changes of outcome measures derived from SST and IST after active rTMS and sham stimulation. Only one significant correlation was found between BIS-11 and IST. It is concluded that rIFG may not be the candidate site for using HF-rTMS to improve control of response inhibition and reflection impulsivity. The findings of the study make a contribution to re-examination of the role of rIFG in impulsivity. The implications of HF-rTMS are considered, and suggestions are made for the outcome measure tasks selected.