Implications of Assist-As-Needed Robotic Step Training after a Complete Spinal Cord Injury on Intrinsic Strategies of Motor Learning

Abstract

Robotic training paradigms that enforce a fixed kinematic control might be suboptimal for rehabilitative training because they abolish variability, an intrinsic property of neuromuscular control (Jezernik et al., 2003). In the present study we introduce "assist-as-needed" (AAN) robotic training paradigms for rehabilitation of spinal cord injury subjects. To test the efficacy of these robotic control strategies to teach spinal mice to step, we divided 27 adult female Swiss-Webster mice randomly into three groups. Each group was trained robotically by using one of three control strategies: a fixed training trajectory (Fixed group), an AAN training paradigm without interlimb coordination (Band group), and an AAN training paradigm with bilateral hindlimb coordination (Window group). Beginning at 14 d after a complete midthoracic spinal cord transection, the mice were trained daily (10 min/d, 5 d/week) to step on a treadmill 10 min after the administration of quipazine (0.5 mg/kg), a serotonin agonist, for a period of 6 weeks. During weekly performance evaluations, the mice trained with the AAN window paradigm generally showed the highest level of recovery as measured by the number, consistency, and periodicity of steps during the testing sessions. In all three measurements there were no significant differences between the Band and the Fixed training groups. These results indicate that the window training approach, which includes loose alternating interlimb coordination, is more effective than a fixed trajectory paradigm with rigid alternating interlimb coordination or an AAN paradigm without any interlimb constraints in promoting robust postinjury stepping behavior.

Training locomotor networks

“…In most of these studies, however, a distinction is not made as to whether the pharmacological agent is actually inducing locomotion vs. changing the physiological state of the spinal cord so that it can generate locomotion when the afferent systems are allowed to control the motor output. In reports of the facilitation of locomotion in response to either strychnine or quipazine, it was clear that the drug itself, at least for the dosages used, did not induce stepping (Cai et al, 2006b;de Leon et al, 1999;Fong et al, 2005). When the hindlimbs were placed on a moving treadmill belt after administration of the drug, however, effective weight-bearing locomotion could be generated.…”

“…To address the question of whether there was an important interactive effect of the pharmacological intervention and the training, we administered the 5-HT receptor agonist quipazine daily to a group of spinal mice that were step trained and to a group that were not trained (Cai et al, 2006b;Fong et al, 2005). The non-trained mice receiving quipazine showed no sustained improvement in stepping over a period of several weeks, whereas the trained mice receiving quipazine showed a significant improvement in stepping ability.…”

“…This way, only when the trajectory deviates from the desired training trajectory greatly, does the robotic device assist the animal back to the target training trajectory. In this experiment (Cai et al, 2006b), one group was assisted such that each leg could operate independently. A second group was assisted with the additional criterion being that the two limbs must function in an alternating, out of phase fashion.…”

“…Thus we are currently using a computational learning model to test our hypothesis that there is an optimal level of variation in the kinematics and dynamics of stepping. We predict that step training related learning will not occur if the pattern is too fixed or too variable (Cai et al, 2006b). 6. Gaining access to the spinal circuitry that can generate locomotion in humans: taking advantage of state-dependent modulation of the spinal circuitry while using afferents as a source of control…”

A Novel Design and Implementation of a 4-DOF Upper Limb Exoskeleton for Stroke Rehabilitation with Active Assistive Control Strategy

“…This is the impedancebase control. To help the movement of patients with minimal helping force, the control strategy call "Assistance-as-need" (AAN) have been presented in ref [14][15] and the potential of AAN strategies has been shown in upper-limb training of stroke patients [16][17]. The challenge-based control strategy will make the movement of the participant limb more difficult or challenging.…”