The Effects of High-Frequency rTMS Over the Left Dorsolateral Prefrontal Cortex on Reward Responsiveness

Background: High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) over the prefrontal region has been shown to increase endogenous dopamine release in the striatum, which is closely associated with probabilistic reward learning. Objective: We attempted to investigate whether HF-rTMS over the dorsolateral prefrontal cortex (DLPFC) would modulate reward responsiveness using a probabilistic reward task. Methods: Eighteen healthy volunteers participated in this study using a randomized within-subject crossover design. Each participant received a single session of 10 Hz high-frequency rTMS over the left DLPFC and another session of sham stimulation, with an interval of 1 week between sessions. Nine hundred magnetic stimuli were delivered in three blocks 10 mm apart, for a total duration of 30 min. After each stimulation session, participants performed a probabilistic reward task where two different stimuli were rewarded with different probabilities (i.e., rich vs. lean) to produce a response bias toward the more frequently rewarded stimulus. Results: Participants showed faster and more accurate responses toward the rich stimulus than the lean stimulus. Participants developed a greater response bias toward the rich stimulus after HF-rTMS during the early learning trials versus after sham stimulation. No differences in response bias were observed during the later learning trials. Reaction time did not differ between the active HF-rTMS and sham stimulation conditions. Conclusion: HF-rTMS over the left DLPFC increased responsiveness toward rewarding stimuli. This facilitation effect of HF-rTMS might be associated with changes in dopaminergic neurotransmission in the striatum. Our findings contribute to our understanding of the effects HF-rTMS can have on reward learning. (C) 2013 Elsevier Inc. All rights reserved.