Dopaminergic manipulations affect the modulation and meta-modulation of movement speed: evidence from two pharmacological interventions

A body of research implicates dopamine in the average speed of simple movements. However, naturalistic movements span a range of different shaped trajectories and rarely proceed at a single constant speed; instead, speed is reduced when drawing "corners" compared to "straights" (i.e., speed-modulation), and the extent of this slowing down is dependent upon the global shape of the movement trajectory (i.e., speed-meta-modulation) - for example whether the shape is an ellipse or a rounded square. By employing two pharmacological intervention studies - individuals with Parkinsons both ON and OFF dopaminergic medication (N = 32) and members of the general population on a D2 receptor blocker (haloperidol) versus placebo (N = 43) - we implicate dopamine in speed, speed-modulation and speed-meta-modulation. Our findings move beyond vigour models implicating dopamine in average movement speed, and towards a conceptualisation that involves the modulation of speed as a function of contextual information.