Abstract T P112: The Effect of Monoaminergic Drugs on Motor Cortex Excitability, Motor Performance and Psychophysics

Abstract

INTRODUCTION: The benefit of pharmacologic augmentation of stroke recovery remains unclear. As post-stroke motor recovery depends on training-dependent plasticity, we wanted to test the effect of these drugs on the excitability of primary motor cortex (M1), kinematic and psychophysical measures. METHODS: Nine able-bodied individuals (4 males) participated in 4 test sessions at least 1 week apart during which they were administered one oral dose of 4 different medications: placebo (P), amphetamine 10mg (A), methylphenidate 20mg (M), carbidopa/levodopa 25/100mg (D). We used transcranial magnetic stimulation (TMS) to measure the effects of the different drugs on M1 excitability. Motor evoked potentials (MEP) were elicited using TMS at intensities of 35-80% of maximum stimulator output. The Boltzmann function was calculated for MEP amplitudes and compared across the 4 drug conditions. The effects of the drugs on psychophysics and movement kinematics were captured by a 2d accelerometer mounted on the dorsum of the hand. We measured the reaction time and the peak acceleration and dispersion of directions of auditory paced ballistic wrist extension movements. RESULTS: Comparison of the 4 different equations for the Boltzmann sigmoid curve where R max represents the maximum MEP amplitude; k, the slope of the curve; and S50, the intensity that produced half of the maximum MEP amplitude revealed significant differences between drug conditions. Compared to P, A led to a significant decrease in the maximum MEP amplitude (p= 0.00015), while D increased it (p=0.013). The other two parameters were similar to placebo. M had no effect on any of the three parameters. The different drugs had no statistically significant effect on the kinematic measures or reaction time. CONCLUSIONS: These results indicate that the neuromodulatory effect of drugs on M1 excitability differs, which may point to different mechanisms mediating the beneficial effects of these drugs on functional recovery after stroke. It would also support the notion that the beneficial effect of the drugs on recovery is likely due to improved kinematics or psychophysics of executions during training.