Parkinsonism Reduces Coordination of Fingers, Wrist, and Arm in Fine Motor Control Hans-Leo Teulings, Jose ´ L. Contreras-Vidal, George E. Stelmach, and Charles H. Adler* Motor Control Laboratory, Arizona State University, Tempe, Arizona 85287-0404; and *Mayo Clinic, Scottsdale, Arizona 85259 This experiment investigates movement coordina- tion in Parkinson’s disease (PD) subjects. Seventeen PD patients and 12 elderly control subjects performed several handwriting-like tasks on a digitizing writing tablet resting on top of a table in front of the subject. The writing patterns, in increasing order of coordina- tion complexity, were repetitive back-and-forth move- ments in various orientations, circles and loops in clockwise and counterclockwise directions, and a com- plex writing pattern. The patterns were analyzed in terms of jerk normalized for duration and size per stroke. In the PD subjects, back-and-forth strokes, involving coordination of fingers and wrist, showed larger normalized jerk than strokes performed using either the wrist or the fingers alone. In the PD patients, wrist flexion (plus radial deviation) showed greater normalized jerk in comparison to wrist extension (plus ulnar deviation). The elderly control subjects showed no such effects as a function of coordination complex- ity. For both PD and elderly control subjects, looping patterns consisting of circles with a left-to-right fore- arm movement, did not show a systematic increase of normalized jerk. The same handwriting patterns were then simulated using a biologically inspired neural network model of the basal ganglia thalamocortical relations for a control and a mild PD subject. The network simulation was consistent with the observed experimental results, providing additional support that a reduced capability to coordinate wrist and finger movements may be caused by suboptimal functioning of the basal ganglia in PD. The results suggest that in PD patients fine motor control problems may be caused by a reduced capability to coordinate the fingers and wrist and by reduced control of wrist flexion. r 1997 Academic Press INTRODUCTION Parkinson’s disease (PD) is caused by the degenera- tion of nigrostriatal neurons resulting in a reduction of the neurotransmitter dopamine (25, 26). Apart from the well-known movement control problems, slowness, reduced movement amplitudes, and prolonged decelera- tion times, PD patients are hypothesized to suffer from difficulties in the coordination and control of various muscle systems (15). For example, PD patients show a delay of the onset of the opening of the hand relative to the initiation of the transportation of the forearm (6). Whereas normal subjects can smoothly modify an ongoing movement, PD patients initiate a corrective movement only after completing the initial movement (15). Temporal dissociation has also been observed between the left and the right arms in PD patients (22). When fingers and thumb of the same arm were ana- lyzed, Benecke et al. (2) found that PD subjects showed a substantial impairment when performing an isotonic elbow flexion while isometrically squeezing a force transducer. Similarly, Isenberg and Conrad (20) ob- served that PD subjects do not initiate components of arm movements simultaneously, resulting in angular or curved movement trajectories. These data suggest that in PD patients coordination is reduced in move- ment patterns that require control of a large number of muscles and joints. PD leads to a disruption in the execution of practiced skills such as handwriting (25, 41). Boisseau et al. (3) observed that PD handwriting can be characterized by various types of dysfluencies: lack of control, abrupt changes of direction, tremor, slowness, hesitation, rigid- ity, variability of baseline, and, in some cases, micro- graphia. The breakdown of handwriting may come from the inadequate control of acceleration amplitude (41), which is also reflected by abnormal EMG ampli- tudes (42) and by reduced coordination of independent movement components (20). Handwriting-like movement patterns are ideal tasks to study motor control because they are well learned. Many potential artifacts due to muscle strength limita- tions, gravity, inertia, visual feedback, and insufficient practice are absent. More importantly, coordination complexity can be varied by using handwriting pat- terns involving different combinations of finger, wrist, and arm movement components. In Western cursive handwriting, finger movements (i.e., flexion and exten- sion of the thumb and the opposing index and middle fingers) generate primarily up-and-down strokes (i.e., EXPERIMENTAL NEUROLOGY 146, 159–170 (1997) ARTICLE NO. EN976507 159 0014-4886/97 $25.00 Copyright r 1997 by Academic Press All rights of reproduction in any form reserved.