Single pulse TMS differentially modulates reward behavior

Greater knowledge of cortical brain regions in reward processing may set the stage for using transcranial magnetic stimulation (TMS) as a treatment in patients with avolition, apathy or other drive-related symptoms. This study examined the effects of single pulse (sp) TMS to two reward circuit targets on drive in healthy subjects. Fifteen healthy subjects performed the monetary incentive delay task (MID) while receiving fMRI-guided spTMS to either inferior parietal lobe (IPL) or supplemental motor area (SMA). The study demonstrated decreasing reaction times (RT) for increasing reward. It also showed significant differences in RT modulation for TMS pulses to the IPL versus the SMA. TMS pulses during the delay period produced significantly more RT slowing when targeting the IPL than those to the SMA. This RT slowing carried over into subsequent trials without TMS stimulation, with significantly slower RTs in sessions that had targeted the IPL compared to those targeting SMA. The results of this study suggest that both SMA and IPL are involved in reward processing, with opposite effects on RT in response to TMS stimulation. TMS to these target cortical regions may be useful in modulating reward circuit deficits in psychiatric populations.