The Neurochemical Mechanisms Underlying the Enhancing Effects of Rewards and Punishments on Motor Performance

Monetary rewards and punishments enhance motor performance and are associated with corticospinal excitability (CSE) increases within the motor cortex (M1) during movement preparation. However, such CSE changes have unclear origins; they could stem from increased glutamatergic (GLUTergic) facilitation and/or decreased type A gamma-aminobutyric acid (GABAA)-mediated inhibition within M1. To investigate this, paired-pulse transcranial magnetic stimulation was used to assess GLUTergic facilitation and GABAA inhibition within M1 whilst participants prepared to execute 4-element finger-press sequences. Behaviourally, rewards and punishments enhanced both reaction and movement times. Neurochemically, regardless of rewards or punishments, a digit-specific increase in GLUTergic facilitation and digit-unspecific decrease in GABAA inhibition occurred during preparation as movement onset approached. In parallel, both rewards and punishments non-specifically increased GLUTergic facilitation, but only rewards non-specifically decreased GABAA inhibition during preparation. This suggests that, to enhance performance, rewards both increase GLUTergic facilitation and decrease GABAA inhibition whilst punishments selectively increase GLUTergic facilitation. A control experiment revealed that such changes were not observed post-movement as participants processed reward and punishment feedback, indicating they were selective to movement preparation. Collectively, these results map the neurochemical changes in M1 by which incentives enhance motor performance.