Dosage-dependent non-linear effect of l-dopa on human motor cortex plasticity

Introduction: The neuromodulator dopamine affects learning and memory formation and their likely physiological correlates, long-term depression and potentiation in animals and humans. It is known from animal experiments that dopamine exerts a dosage-dependent, inverted U-shaped effect on these functions. However, this has not been explored in humans so far. Methods: In order to reveal a non-linear dose-dependent effect of dopamine on cortical plasticity in humans, we explored the impact of 25, 100, and 200mg of the dopamine precursor l-dopa on transcranial direct current stimulation (tDCS) -induced plasticity in…