Abstract
A wealth of evidence describes the strong positive impact that reward has on motor control at the behavioural level. However, surprisingly little is known regarding the neural mechanisms which underpin these effects, beyond a reliance on the dopaminergic system. In recent work, we developed a task that enabled the dissociation of the selection and execution components of an upper limb reaching movement. Our results demonstrated that both selection and execution are concommitently enhanced by immediate reward availability. Here, we investigate what the neural underpinnings of each component may be. To this end, we aimed to alter the cortical excitability of the ventromedial prefrontal cortex and supplementary motor area using continuous theta-burst transcranial magnetic stimulation (cTBS) in a within-participant design (N = 23). Both cortical areas are involved in determining an individual’s sensitivity to reward and physical effort, and we hypothesised that a change in excitability would result in the reward-driven effects on action selection and execution to be altered, respectively. To increase statistical power, participants were pre-selected based on their sensitivity to reward in the reaching task. While reward did lead to enhanced performance during the cTBS sessions and a control sham session, cTBS was ineffective in altering these effects. These results may provide evidence that other areas, such as the primary motor cortex or the premotor area, may drive the reward-based enhancements of motor performance.
Highlights
In saccadic eye movements, reward has a well-known ability to invigorate motor control, enhance accuracy, and promote accurate action selection in the face of potential distractors (Kojima and Soetedjo 2017; Manohar et al 2015; Sohn and Lee 2006; Takikawa et al 2002)
Reward led to faster reaction times ( F(1,22) = 8.18, p = 0.009, partial 2 = 0.37 ; Fig. 1a), whilst improving selection accuracy ( F(1,22) = 16.7, p < 0.001, partial 2 = 0.76 ; Fig. 1b), clearly demonstrating that the selection component benefited from the presence of reward
This suggests that continuous theta-burst transcranial magnetic stimulation (cTBS) over ventro-medial prefrontal cortex (vmPFC) or supplementary motor area (SMA) had no effect on behaviour
Summary
Reward has a well-known ability to invigorate motor control, enhance accuracy, and promote accurate action selection in the face of potential distractors (Kojima and Soetedjo 2017; Manohar et al 2015; Sohn and Lee 2006; Takikawa et al 2002). We extended these behavioural findings from eye movements to reaching movements (Codol et al 2020). We aimed to investigate which cortical regions are involved in the reward-based enhancement of motor performance using transcranial magnetic stimulation (TMS)
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