Dual modulating effects of amphetamine on neuronal excitability and stimulation-induced plasticity in human motor cortex. |
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Authors: | Ulf Ziemann Alda Tam Cathrin Bütefisch Leonardo G Cohen |
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Institution: | Human Cortical Physiology Section, NINDS, National Institutes of Health, Building 10, Bethesda, MD 20892, USA. u.ziemann@em.uni-frankfurt.de |
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Abstract: | 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 measure 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 10mg 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 ( approximately 10 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. |
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