Remapping residual coordination for controlling assistive devices and recovering motor functions

Abstract

The concept of human motor redundancy attracted much attention since the early studies of motor control, as it highlights the ability of the motor system to generate a great variety of movements to achieve any single well-defined goal. The abundance of degrees of freedom in the human body may be a fundamental resource in the learning and remapping problems that are encountered in human–machine interfaces (HMIs) developments. The HMI can act at different levels decoding brain signals or body signals to control an external device. The transformation from neural signals to device commands is the core of research on brain-machine interfaces (BMIs). However, while BMIs bypass completely the final path of the motor system, body-machine interfaces (BoMIs) take advantage of motor skills that are still available to the user and have the potential to enhance these skills through their consistent use. BoMIs empower people with severe motor disabilities with the possibility to control external devices, and they concurrently offer the opportunity to focus on achieving rehabilitative goals. In this study we describe a theoretical paradigm for the use of a BoMI in rehabilitation. The proposed BoMI remaps the user’s residual upper body mobility to the two coordinates of a cursor on a computer screen. This mapping is obtained by principal component analysis (PCA). We hypothesize that the BoMI can be specifically programmed to engage the users in functional exercises aimed at partial recovery of motor skills, while simultaneously controlling the cursor and carrying out functional tasks, e.g. playing games. Specifically, PCA allows us to select not only the subspace that is most comfortable for the user to act upon, but also the degrees of freedom and coordination patterns that the user has more difficulty engaging. In this article, we describe a family of map modifications that can be made to change the motor behavior of the user. Depending on the characteristics of the impairment of each high-level spinal cord injury (SCI) survivor, we can make modifications to restore a higher level of symmetric mobility (left versus right), or to increase the strength and range of motion of the upper body that was spared by the injury. Results showed that this approach restored symmetry between left and right side of the body, with an increase of mobility and strength of all the degrees of freedom in the participants involved in the control of the interface. This is a proof of concept that our BoMI may be used concurrently to control assistive devices and reach specific rehabilitative goals. Engaging the users in functional and entertaining tasks while practicing the interface and changing the map in the proposed ways is a novel approach to rehabilitation treatments facilitated by portable and low-cost technologies.

Reorganization of finger coordination patterns through motor exploration in individuals after stroke

“…This property of body-machine interfaces has typically been used for the control of assistive devices for persons with limited mobility [ 43 – 45 ]. However, the current results support recent evidence that these interfaces can also be used as a rehabilitation tool to improve the movement kinematics [ 46 , 47 ] as well alter abnormal muscle activity [ 48 ].…”

Body-Machine Interfaces after Spinal Cord Injury: Rehabilitation and Brain Plasticity

“…These functional findings are consistent with earlier studies showing increased MMT and force output on cervical SCI participants practicing upper-body motions with a different BMI based on optical sensors and principal component analysis [43,44]. Here, we found that practice with the BMI also induced increases in FA values in one area that had shown lower FA in SCI subjects than controls, the left cingulum.…”

“…Moreover, a protocol that combines BMI use with traditional exercises for rehabilitation could potentially result in even stronger rehabilitative effects. The benefit of BMIs that use VR is that they can provide an extensive range of enjoyable environments where people can sustain the motivation to practice for extended periods of time [44,71]. Another benefit of this BMI is the ability to measure relatively small changes in movements that do not require a significant amount of effort by the subject.…”

Learning new movements after paralysis: Results from a home-based study

“…1a) (see also 15, 16 ). Specifically sensor 1 was on the left arm, sensor 2 on the left shoulder, sensor 3 on the right shoulder and sensor 4 on the right arm.…”