Spontaneous and intentional dynamics of bimanual coordination in Parkinson's disease Winston D. Byblow a, * , Jeery J. Summers b , Julie Thomas c a Human Motor Control Laboratory, Department of Sport and Exercise Science, University of Auckland, Private Bag 92019, Auckland, New Zealand b Department of Psychology, University of Tasmania, Hobart, Tasmania, Australia c Department of Psychology, University of Southern Queensland, Toowoomba, Qld, Australia Abstract The aim of this study was to investigate the coordination dynamics of individuals with Parkinson's disease (Pd) during the production of rhythmic pronation and supination movements of the upper limb in symmetric (inphase) and asymmetric (antiphase) patterns, and dynamics associated with intentional switching between patterns. Participants with Pd (n  4) and age-matched controls (n  3) exhibited spontaneous phase transitions from antiphase to inphase patterns at an individually speci®c movement frequency (STF). In metronome-paced trials subjects produced antiphase or inphase patterns at ®ve frequencies ranging from STF )0.5 to STF +0.5 Hz. In a second session the same participants produced intentional tran- sitions (inphase to antiphase, antiphase to inphase) at the four highest frequencies. Partici- pants with Pd exhibited spontaneous transitions at a lower frequency than age-matched controls. The Pd group tended to deviate from intended relative phase relations to a greater extent than controls, resulting in signi®cantly higher asynchrony between hands for the Pd group. Normalised to STF there was equivalence between patients and controls in terms of uniformity (stability) of relative phase, despite the asynchrony. Although no clear dierences between the Pd and control participants were found in the transition duration for intentional switching, the time between the signal to switch and the transition onset was longer for the Pd participants than the controls. This ®nding supports the suggestion that individuals with Pd Human Movement Science 19 (2000) 223±249 www.elsevier.com/locate/humov * Corresponding author. Fax: +64-9-373-7043. E-mail address: w.byblow@auckland.ac.nz (W.D. Byblow). 0167-9457/00/$ - see front matter Ó 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 9 4 5 7 ( 0 0 ) 0 0 0 1 1 - 7