Parkinson bradykinesia correlates with EEG background frequency and perceptual forward projection

Background: To deal with processing-time in the nervous system, visuomotor control requires anticipation. An index for such anticipation is provided by the 'flash-lag illusion' in which moving objects are perceived ahead of static objects while actually being in the same place. We investigated the neurophysiological relation between visuomotor anticipation and motor velocity in Parkinson's disease (PD) and controls. Methods: Motor velocity was assessed by the number of keystrokes in 30s ('kinesia score') and visuomotor anticipation in a behavioural flash-lag paradigm while electroencephalography data was obtained. PD patients (n=24) were divided in a 'PDslow' and a 'PDfast' group based on kinesia score. Results: The PDslow group had a lower kinesia score than controls (resp. 40.3±1.7 and 64.9±4.6, p<0.001). The flash-lag illusion was weaker in the PDslow group than in controls (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 flash-lag illusion correlated with the kinesia score (cc=0.45, p=0.02). Finally, electroencephalography background frequency was lower in the PDslow group than in controls (resp 8.24±0.24 and 9.1±0.32Hz, p=0.01) and background frequency correlated with the kinesia score (cc=0.58, p=0.001). Conclusions: The decreased flash-lag illusion and lower electroencephalography background frequency in more bradykinetic PD patients provides support for disturbed visuomotor anticipations, putatively caused by reduced, sub-cortically mediated, network efficiency. This suggests a link between anticipation in early-stage visual motion processing and motor preparation.