Velocity control in Parkinson’s disease: a quantitative analysis of isochrony in scribbling movements

Abstract

An experiment was conducted to contrast the motor performance of three groups (N = 20) of participants: (1) patients with confirmed Parkinson Disease (PD) diagnose; (2) age-matched controls; (3) young adults. The task consisted of scribbling freely for 10 s within circular frames of different sizes. Comparison among groups focused on the relation between the figural elements of the trace (overall size and trace length) and the velocity of the drawing movements. Results were analysed within the framework of previous work on normal individuals showing that instantaneous velocity of drawing movements depends jointly on trace curvature (Two-thirds Power Law) and trace extent (Isochrony principle). The motor behaviour of PD patients exhibited all classical symptoms of the disease (reduced average velocity, reduced fluency, micrographia). At a coarse level of analysis both isochrony and the dependence of velocity on curvature, which are supposed to reflect cortical mechanisms, were spared in PD patients. Instead, significant differences with respects to the control groups emerged from an in-depth analysis of the velocity control suggesting that patients did not scale average velocity as effectively as controls. We factored out velocity control by distinguishing the influence of the broad context in which movement is planned--i.e. the size of the limiting frames--from the influence of the local context--i.e. the linear extent of the unit of motor action being executed. The balance between the two factors was found to be distinctively different in PD patients and controls. This difference is discussed in the light of current theorizing on the role of cortical and sub-cortical mechanisms in the aetiology of PD. We argue that the results are congruent with the notion that cortical mechanisms are responsible for generating a parametric template of the desired movement and the BG specify the actual spatio-temporal parameters through a multiplicative gain factor acting on both size and velocity.

Altered Perceptual Sensitivity to Kinematic Invariants in Parkinson's Disease

“…As the differences between patients and controls were not restricted to a certain path nor a certain speed, they were probably not due to abnormalities in spatial perception nor to the geometry of the elliptical paths [57], [58]. Rather, these differences appear to represent a more global deficit in how visual motion is perceived in PD.…”

Prehension synergies and hand function in early-stage Parkinson’s disease

“…As mentioned in the Introduction, changes in hand function are among the relatively early symptoms of PD (McLennan et al 1972; Viviani et al 2009). Our previous studies showed significant changes in multi-finger synergy indices and ASAs during pressing tasks even in patients at stage-I PD (Park et al 2012, 2014).…”

“…Although hand motor dysfunction is a well-documented early consequence of Parkinson’s disease (PD, e.g., micrographia, McLennan et al 1972; Viviani et al 2009), problems with finger coordination are not mentioned among the cardinal signs of PD. A series of recent studies in patients with early-stage PD documented changes in finger interaction and coordination indices during isometric force production tasks (Park et al 2012, 2013a, 2014).…”

Quantitative assessment of motor abnormalities in untreated patients with major depressive disorder

“…One important feature of programmed motor behavior is the principle of isochrony, which refers to the relationship between distance and velocity of hand movements during limb movement. Isochrony stipulates that the average velocity of endpoint movement increases with movement distance (hence preserving the time span, making it isochronous ), and is present in many if not most types of movement (Viviani et al, 2009; Viviani and Flash, 1995). For example, when moving the elbow to different degrees of flexion, normal healthy individuals will scale movement velocity in proportion to degrees of flexion, thus maintaining a constant movement time.…”