Time perception reflects individual differences in motor and non-motor symptoms of Parkinson's disease.

Decreasing dopaminergic function is at the core of Parkinson's disease (PD) motor symptoms and changes in dopaminergic action are associated with many comorbid non-motor symptoms in PD. Notably, dopaminergic signaling in the striatum has been shown to play a critical role in the perception of time. We hypothesize that patients with PD perceive time differently and in accordance with their specific comorbid non-motor symptoms and clinical state. This means that individual differences in clinical symptoms may be reflected in individual differences in timing behavior. To test this hypothesis, we recruited patients with PD and compared individual differences in patients' clinical state with their ability to judge intervals of time ranging from 500 ms to 1100 ms while on and off their prescribed dopaminergic medications. We show that medication state (on vs. off medications) did not affect timing behavior, but individual differences in timing behavior are able to predict individual differences in comorbid non-motor symptoms, duration of PD diagnosis, and prescribed dopaminergic medications. We show that comorbid impulse control disorder is associated with temporal overestimation; depression is associated with decreased temporal accuracy; and increased PD duration and prescribed levodopa monotherapy are associated with reduced temporal precision and accuracy. Observed differences in time perception are consistent with hypothesized dopaminergic mechanisms thought to underlie the respective motor and non-motor symptoms in PD. In future work, time perception tasks may augment clinical diagnosis strategies, or help disentangle the neural and cognitive mechanisms underlying PD motor and non-motor symptom etiology.