Dual modulating effects of amphetamine on neuronal excitability and stimulation-induced plasticity in human motor cortex

Objectives: The objective of the present study is to test the modulating effects of dextro-amphetamine (d-AMP) on excitability and stimulation-induced plasticity in human motor cortex. Methods: Transcranial magnetic stimulation (TMS) was used to treasure motor threshold, motor evoked potential (MEP) size and paired-pulse intracortical facilitation (ICF) in the biceps muscle of 7 healthy subjects before and after two different experimental manipulations: temporary forearm ischemic nerve block (INB) alone, or INB plus 0.1 Hz repetitive TMS (INB + rTMS) of the motor cortex contralateral to INB. Both manipulations were run after treatment with 10 mg of d-AMP or placebo (PBO). Results: In the PBO experiments, INB alone had no significant effect on MEP size or ICF, while INB + rTMS produced long-lasting (>60 min) increases. Compared with PBO, d-AMP led to a short-lasting (similar to10 min) increase in MEP size in the INB alone experiment, but suppressed the long-lasting increases of MEP size and ICF in the INB + rTMS experiment. Conclusions: The present findings suggest that d-AMP increases neuronal excitability but suppresses long-lasting stimulation-induced plasticity in human motor cortex. These dual effects may be relevant when using d-AMP to modulate human cortex function, (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.