Effects of accuracy constraints on reach-to-grasp movements in cerebellar patients

Abstract

Reach-to-grasp movements of patients with pathology restricted to the cerebellum were compared with those of normal controls. Two types of paradigms with different accuracy constraints were used to examine whether cerebellar impairment disrupts the stereotypic relationship between arm transport and grip aperture and whether the variability of this relationship is altered when greater accuracy is required. The movements were made to either a vertical dowel or to a cross bar of a small cross. All subjects were asked to reach for either target at a fast but comfortable speed, grasp the object between the index finger and thumb, and lift it a short distance off the table. In terms of the relationship between arm transport and grip aperture, the control subjects showed a high consistency in grip aperture and wrist velocity profiles from trial to trial for movements to both the dowel and the cross. The relationship between the maximum velocity of the wrist and the time at which grip aperture was maximal during the reach was highly consistent throughout the experiment. In contrast, the time of maximum grip aperture and maximum wrist velocity of the cerebellar patients was quite variable from trial to trial, and the relationship of these measurements also varied considerably. These abnormalities were present regardless of the accuracy requirement. In addition, the cerebellar patients required a significantly longer time to grasp and lift the objects than the control subjects. Furthermore, the patients exhibited a greater grip aperture during reach than the controls. These data indicate that the cerebellum contributes substantially to the coordination of movements required to perform reach-to-grasp movements. Specifically, the cerebellum is critical for executing this behavior with a consistent, well-timed relationship between the transport and grasp components. This contribution is apparent even when accuracy demands are minimal.

Extending the mirror neuron system model, I

“…Bennett and Castiello (1994) found the mean duration of a reach-to-grasp movement to a target object 35 cm away to be 844 ms (SD = 140) for healthy control subjects. Rand et al (2000) found the mean duration of a 40 cm reach-to-grasp movement to be 784.4 ms (SEM = 67.75) for healthy controls. Therefore, each time step of a simulated grasp corresponds to approximately 25-30 ms. After the completion of each grasp, the visual hand state was calculated for ten more time steps, simulating observation of a static grasp for 250-300 ms.…”

Effect of speed manipulation on the control of aperture closure during reach-to-grasp movements

“…Thus, the aperture width appeared to be modified in relation to the temporal characteristics of the transport component. When reach-to-grasp movements were performed under various transport durations or speeds, the maximum aperture occurred at a relatively fixed timing in relation to overall movement duration (Paulignan et al 1991a;Marteniuk et al 1990;Rand et al 2000;Smeets and Brenner 1999;Wallace and Weeks 1988;Wallace et al 1990). However, some other studies demonstrated that the duration for aperture closure movement was unaffected by different task conditions (Bootsma and van Wieringen 1992;Gentilucci et al 1992;Paulignan et al 1991b;Watson and Jakobson 1997;Zaal et al 1998).…”

Control of aperture closure during reach-to-grasp movements in parkinson’s disease

“…There have been numerous observations indicating that the moment of the maximum grip aperture (the time at which the distance between the thumb and index fingers is maximized) is precisely timed with respect to hand transport (Jeannerod 1984;Marteniuk et al 1990;Rand et al 2000;Wallace et al 1990). For this reason, it has been suggested that those two processes are temporally linked (Hoff and Arbib 1993;Jeannerod 1981Jeannerod , 1984.…”