Repetitive transcranial magnetic stimulation to right prefrontal cortex does not modulate the psychostimulant effects of amphetamine

Preliminary evidence indicates lateralized efficacy of repetitive transcranial magnetic stimulation (rTMS) in the treatment of mood disorders. Right-sided prefrontal cortex (PFC) stimulation has been reported to treat symptoms of mania. The acute effect of amphetamine serves as a model of mania in healthy individuals, hence rTMS to right PFC was hypothesized to attenuate the psychostimulant action of amphetamine in healthy volunteers. Eighteen subjects received rTMS to right PFC or right parietal cortex (PAR), or sham stimulation, in a randomized between-subjects design. Following rTMS subjects received i.v. amphetamine (0.15 mg/kg). Intravenous amphetamine induced robust subjective (visual analogue scales) and objective (blood pressure, sustained attention) effects, but the extent of the effects was not modulated by right PFC stimulation. Though this dose cannot refute the efficacy of rTMS in treating mania, it indicates that any therapeutic mechanism of action is unlikely to be through modulation of dopamine function.