Oral Sessions

Background: To deal with the delay of processing-time in the nervous system, visuomotor control requires anticipation.An index for such anticipation is provided by the ‚flash-lag illusion' (FLI) in which moving objects are perceived ahead of static objects while actually being in the same place.Methods: To gain further insight in the neurophysiological relation between visuomotor anticipation and motor velocity itself, we assessed these two parameters together with EEG background frequency and compared Parkinson's disease (PD) patients and healthy volunteers (HV).Motor velocity was quantified by the number of keystrokes in 30s ('kinesia score', KS).PD patients (n = 24) were divided in a 'PDslow' and a 'PDfast' group based on KS.Stimulus presentation.a. Participants watched a ball rotating in clockwise direction with a velocity of 540°/s.In a range of 90° (45° below and 45° above the horizon), corresponding with -83 and +83ms relative to the position of the moving ball Results:The PDslow group had a lower KS than HV (resp.40.3±1.7 and 64.9±4.6,p<0.001).The FLI was lower in the PDslow group than in HV (resp.fractions 0.32±0.04 and 0.50±0.09 of the responses indicating perceived lagging, p=0.03).Furthermore, the magnitude of the FLI correlated with the KS (cc=0.45,p=0.02).Finally, EEG background frequency was lower in the PDslow group than in HV (resp 8.24±0.24and 9.1±0.32Hz, p=0.01) and background frequency correlated with the KS score (cc=0.58,p=0.001).Response profiles of the different groups on the Flash Lag task.On the x-axis the position of the moving ball at the appearance of the flash relative to the horizon and converted to milliseconds (ms) based on its velocity.Relation between EEG background velocity and motor velocity.correlation between EEG background velocity (in Hz) and the amount of key presses / 30 sec for the PDslow, PDfast and HV group together (black) and apart (resp red, blue, green). Conclusion:The decreased FLI and lower EEG background frequency in more bradykinetic PD patients provides support for disturbed visuomotor anticipations, which might be caused by reduced, sub-cortically mediated, network efficiency.This suggests a link between anticipation in early-stage visual motion processing and motor preparation.