Functional reorganization of upper-body movement after spinal cord injury

Abstract

Survivors of spinal cord injury need to reorganize their residual body movements for interacting with assistive devices and performing activities that used to be easy and natural. To investigate movement reorganization, we asked subjects with high-level spinal cord injury (SCI) and unimpaired subjects to control a cursor on a screen by performing upper-body motions. While this task would be normally accomplished by operating a computer mouse, here shoulder motions were mapped into the cursor position. Both the control and the SCI subjects were rapidly able to reorganize their movements and to successfully control the cursor. The majority of the subjects in both groups were successful in reducing the movements that were not effective at producing cursor motions. This is inconsistent with the hypothesis that the control system is merely concerned with the accurate acquisition of the targets and is unconcerned with motions that are not relevant to this goal. In contrast, our findings suggest that subjects can learn to reorganize coordination so as to increase the correspondence between the subspace of their upper-body motions with the plane in which the controlled cursor moves. This is effectively equivalent to constructing an inverse internal model of the map from body motions to cursor motions, established by the experiment. These results are relevant to the development of interfaces for assistive devices that optimize the use of residual voluntary control and enhance the learning process in disabled users, searching for an easily learnable map between their body motor space and control space of the device.

Arm weight support training improves functional motor outcome and movement smoothness after stroke

“…Jerk, i.e. the time derivative of acceleration, has been used as an empirical measure of movement smoothness (Casadio et al, 2010). In this study, NJ was tested as a measure of the quality of selective motor control and was used to evaluate the qualitative features of the multi-joint upper limb movements, considering its inverse correlation with the smoothness of hand movement (Flash and Hogan, 1985;Caimmi et al, 2008).…”

“…The velocity threshold was 5% of the maximum velocity achieved by the subject during the whole second motor task session. -normalized jerk (NJ) (without dimension): square root of the jerk [j(t), norm of the third time derivative of the hand marker position], averaged over the entire catching/returning movement duration and normalized with respect to T and L (Casadio et al, 2010). This measure is sensitive to smoothness, with larger jerk values corresponding to less smoothness.…”

Body machine interface: Remapping motor skills after spinal cord injury

“…We developed a body-machine interface that provides impaired individuals with a continuous signal space operated directly by the combination of residual motions that the users are most capable of controlling [6]. Here, we used this interface for engaging subjects in virtual reality games that trained specific control actions.…”

“…The control space u had reduced dimension with respect to the body signal space h, thus we can decompose the body signals into their "null-space" components that do not change the control vector, and the orthogonal "task space" components that determine the value of the command vector [6][7]. At the same time this mapping offers a large variety of specifications.…”

“…Therefore, it is important to understand and facilitate the reorganization of residual motions for the control of powered wheelchairs and other assistive devices after spinal cord injury, through a user specific approach. Hence, we have developed a novel body-machine interface [6] based on two key concepts:…”