Temporal Expectations in Parkinson's Disease

Overview

Although major progresses were realized during recent years, temporal cognition is still poorly understood. However, abnormal temporal cognition is an underestimated aspect of several neurological disorders, particularly if basal ganglia (BG) are affected. Therefore, the interest of studying temporal cognition is double: firstly, it is an essential function necessary to guide all behavior; secondly, it seems to be very sensitive to the integrity of dopaminergic pathways. It is well known that Parkinson's disease (PD) is partly due to a degeneration of neurons producing dopamine in the Substantia Nigra pars compacta (SNc). Therefore, in this project, PD patients and healthy volunteers will be used as a model to study the role of dopamine in temporal expectation. An expectation is an internal representation of an event that is likely to occur in the future. Temporal expectation builds-up as time elapses before the upcoming event. The role of temporal expectation in the oculomotor domain has often been studied using anticipatory eye movements as a tool. Indeed, expectation evokes anticipatory eye movements. However, to the knowledge of the investigators, expectation and anticipation have so far been studied in experimental tasks where temporal information is essential but not voluntarily controlled. This is usually referred to as 'automatic' or 'emergent' timing: the timing of the eye movement adapts to the timing of the target, implicitly and without voluntary control of the subject. However, anticipatory movements can also be based on an explicit estimation of time, e.g. during music playing. In summary, timing can be based on cognitive (explicit) or automatic (implicit) processing. The originality of the behavioral task the investigators will use in this study is that it will require an explicit comparison of a memorized duration with elapsing time in order to anticipate target appearance. In this task, expectation of the upcoming event will build up on explicit temporal information. Same PD patients will be tested under treatment ("ON") and without treatment ("OFF") to determine the effect of dopamine in time expectation . Only levodopa responsive Parkinson patients will be included and among them only those receiving levodopa and/or dopa agonists three times daily at a stable dosis since 30 days. the investigators hypothesize that eye movements latency will not linearly covary with objective time in "OFF" PD patients. In treated PD patients, a recovery of the linear relationship between subjective and objective time is expected. This would clearly demonstrate the role of dopamine in temporal expectation in humans.