Dopaminergic Manipulation of Adaptation to Intrinsic Task Goals and Extrinsic Task Errors
Creators: name: Leow, Li-Ann
name: Ashley, Tan
name: Carroll, Timothy
name: Dux, Paul
name: Filmer, Hannah
Publisher: name: Open Science Framework
Year: 2022
Subjects: subject: Social and Behavioral Sciences
subject: Life Sciences

description: In a previous study (under preparation), we investigated the role of dopamine in modulating motor performance when completing a task that varied in demands for cognitive effort. We used a motor version of the mental rotation task, where participants were instructed to re-aim by pre-specified angles (0, 30, 60, 135, 150, 160 degrees) away from targets that appeared in unpredictable locations (Georgopoulos &amp; Massey, 1987). To motivate participants to re-aim, targets “jumped” mid-movement at that instructed angle, resulting in target-misses. Participants could only hit the target by successfully re-aiming by that instructed angle. Compared to placebo, participants who consumed levodopa showed slower reaction times and slower peak movement velocities with increasing cognitive load (larger re-aiming angles), particularly for larger, more cognitively effortful re-aiming angles. One interpretation of these results is that increasing dopamine availability with Levodopa altered sensitivity to target-misses, resulting in a preference for slower, more cautious re-aiming. In a target-hitting task, target-misses might serve as a form of reward prediction error: we expect to hit the target as we plan our movements, and when the target jumps mid-movement, we do not receive the expected reward of hitting the target. The proposal that dopamine modulates performance in response to reward prediction errors in the form of target-misses is broadly consistent with extant evidence of the role for dopamine in processing reward prediction errors (for reviews, see Schultz, 2016; Lerner et al., 2021). For example, pharmacological manipulations of dopamine using Levodopa alters responses to reward prediction errors both in neurologically intact adults (Kroemer et al., 2019) and in Parkinson’s disease patients (Sharp et al., 2016). We do not, however, yet know whether levodopa altered the processing of extrinsically defined target errors, or whether levodopa modulated participant’s intrinsic motivation to achieve task goals. Indeed, recent evidence suggested that striatal responses to reward prediction errors, as measured using fMRI, are actually more consistent with failures to attain intrinsically defined task goals (i.e., goal errors) than reward prediction errors (Frömer et al., 2019). Previous research has primarily focussed on how extrinsic rewards affect motor performance (e.g., Manohar et al., 2015; Carroll et al., 2019; Codol et al., 2019). Such extrinsic rewards might directly affect motor performance, and/or affect motor performance indirectly, by altering intrinsic motivation. In this work, we ask the following questions. First, how do extrinsic rewards and intrinsic motivation alter motor performance during exertion of cognitive effort? Second, what is the role of dopamine in determining sensitivity to extrinsic rewards and intrinsic motivation when exerting cognitive effort? In a motor version of the mental rotation task, participants were explicitly instructed to re-aim away from presented targets by pre-defined re-aiming angles (Georgopoulos &amp; Massey, 1987), where larger rotation angles require more cognitive effort. Participants were assigned to one of two possible conditions: (1) a target-disappear condition, where there was no possibility of being rewarded by target-hits as targets always disappeared mid-movement, thus behaviour is driven mainly by intrinsic motivation to achieve task goals; and (2) a target-jump condition, where targets jumped mid-movement by the instructed re-aiming angle, and participants were rewarded with target hits and avoided target-misses when they successfully re-aimed by the instructed angle. Participants could be motivated by both extrinsic rewards and intrinsic motivation in this condition. Based on previous evidence (e.g., Manohar et al., 2015; Carroll et al., 2019; Codol et al., 2019), we expect that extrinsic rewards (i.e., target hits/target misses) will alter motor performance, by speeding reaction times and/or increasing re-aiming accuracy in comparison to the target-disappear condition. Hypotheses 1. If dopamine alters motor performance by modulating intrinsic motivation, then manipulating dopamine with Levodopa will affect motor performance to a similar extent regardless of the absence/presence of extrinsically defined task errors (target-hits/target misses). Alternatively, if the effect of dopamine on motor performance primarily relies on the presence of extrinsically defined errors, then dopamine will alter motor performance to a greater extent in the presence of extrinsic task errors (i.e., target-misses resulting from the target-jump manipulation) than in the absence of extrinsic task errors (i.e., in the target-disappear condition).