The effects of noradrenergic stimulation on the human motor system in healthy subjects

In this study, we investigated the effects of noradrenergic stimulation on the human motor system in healthy subjects assessing both changes in motor performance and changes in neural activity using functional magnetic resonance imaging (fMRI). Evidence from both animal and patient studies suggested that noradrenergic stimulation may enhance motor recovery after brain lesions (e.g., stroke). Furthermore, it was demonstrated that stimulating the motor system with noradrenaline (NA) enhancing drugs may also increase corticomotor excitability in healthy subjects. However, the mechanisms underlying the beneficial effects of noradrenaline on mammalian motor system are still poorly understood, especially in humans. To investigate this issue, we combined several motor behavioral tasks with different complexity such as finger tapping and visuomotor coordination tasks and an fMRI test with a joystick task to assess the effects of noradrenaline on behavior and neural activity. Reboxetine, a selective noradrenaline reuptake inhibitor (SNRI), was used as a noradrenergic stimulant with a double-blinded and placebo-controlled protocol in this study. The motor behavioral results showed that especially visuomotor abilities but not simple motor performance were improved after administration of 8mg Reboxetine compared to placebo. The fMRI results displayed that under Reboxetine neural activity was increased in visual cortex, in predominantly right-hemispheric motor areas, in the right thalamus, in the bilateral putamen and in the right intraparietal areas. In conclusion, our results suggest that noradrenergic stimulation has specific effects on motor behavior which is accompanied by stronger activation in visuomotor information processing areas. The specific effects on motor behavior and neural activity of noradrenergic stimulation in motor recovery of stroke patients will be further investigated to assess its medical usage in neurological rehabilitation.