Fast and precise reaching after stroke: theoretical considerations on motor control
Dr Liesjet VAN DOKKUMa, Prof Denis MOTTETb, Dr Jerome FROGERc, Dr Abdelkader GOUAICHd, Prof Isabelle LAFFONTe
a CHU Montpellier, Gui de Chauliac, b Montpellier University, Movement 2 Health - Euromov, c CHU Nimes, le Grau du Roi, d Montpellier University, LIRMM, e CHU Montpellier, Lapeyronie
Objective: Evaluate the fast and precise reaching capacity post-stroke over various orientations based on Fitts' law that predicts that the movement time increases linearly with the quantity of information transmitted during task performance (1).
Methods: 19 people chronic post-stroke and 19 healthy young controls performed twice a discrete pointing task over 5 orientations with different target sizes. The parameters of Fitts, linear relationship between movement time and task diffulty as well as the corresponding kinematics were calculated.
Results: People post-stroke exhibit a lower information rate, as identified by a steeper slope and the occurrence of a negative intercept showed that the relationship was influenced by non-informational aspects. Movements post-stroke were marked by an increased segmentation, a less direct trajectory and the first velocity peak occurred later in time.
Discussion: Patients after stroke generally followed Fitts’s law, albeit with an expected lower information rate and more variability. Additionally, we found that patients after a stroke exhibited systematic deviations from the informational predictions. We address these deviations based on the nature of the deficit. During pointing movements, healthy people combine feedforward and feedback information to successfully arrive at the target (2). If feedforward is less reliable (because the link between the command and the output is more variable), one will depend more on visual feedback. The kinematic characteristics of the pointing movements of patients subscribed this theoretical deduction: we found a serial enchainment of submovements towards the target, indicating that patients have been waiting for feedback information before adapting and continuing their movement. This behaviour largely accounts for the deviations of the Fitts’s law for patients after a stroke.
1 Fitts PM (1954). The information capacity of the human motor system in controlling the amplitude of movement. J. Exp Psy 47: 381-391.
2 Loram ID, Gollee H, Lakie M, Gawthrop PJ (2011) Human control of an inverted pendulum: is continuous control necessary? Is intermittent control effective? Is intermittent control physiological? J Physiol 589:307 -24
Keywords : Stroke, upper-limb, Fitts law, motor control