Teaching Adult Rats Spinalized as Neonates to Walk Using Trunk Robotic Rehabilitation: Elements of Success, Failure, and Dependence.

UNLABELLED: Robot therapy promotes functional recovery after spinal cord injury (SCI) in animal and clinical studies. Trunk actions are important in adult rats spinalized as neonates (NTX rats) that walk autonomously. Quadrupedal robot rehabilitation was tested using an implanted orthosis at the pelvis. Trunk cortical reorganization follows such rehabilitation. Here, we test the functional outcomes of such training. Robot impedance control at the pelvis allowed hindlimb, trunk, and forelimb mechanical interactions. Rats gradually increased weight support. Rats showed significant improvement in hindlimb stepping ability, quadrupedal weight support, and all measures examined. Function in NTX rats both before and after training showed bimodal distributions, with "poor" and "high weight support" groupings. A total of 35% of rats initially classified as "poor" were able to increase their weight-supported step measures to a level considered "high weight support" after robot training, thus moving between weight support groups. Recovered function in these rats persisted on treadmill with the robot both actuated and nonactuated, but returned to pretraining levels if they were completely disconnected from the robot. Locomotor recovery in robot rehabilitation of NTX rats thus likely included context dependence and/or incorporation of models of robot mechanics that became essential parts of their learned strategy. Such learned dependence is likely a hurdle to autonomy to be overcome for many robot locomotor therapies. Notwithstanding these limitations, trunk-based quadrupedal robot rehabilitation helped the rats to visit mechanical states they would never have achieved alone, to learn novel coordinations, and to achieve major improvements in locomotor function. SIGNIFICANCE STATEMENT: Neonatal spinal transected rats without any weight support can be taught weight support as adults by using robot rehabilitation at trunk. No adult control rats with neonatal spinal transections spontaneously achieve similar changes. The robot rehabilitation system can be inactivated and the skills that were learned persist. Responding rats cannot be detached from the robot altogether, a dependence develops in the skill learned. From data and analysis here, the likelihood of such rats to respond to the robot therapy can also now be predicted. These results are all novel. Understanding trunk roles in voluntary and spinal reflex integration after spinal cord injury and in recovery of function are broadly significant for basic and clinical understanding of motor function.

A bidirectional model of postural sway using force plate data.

This work was designed to expand on our previous anterior-posterior postural control model to include medial-lateral sway of unperturbed posture during quiet standing. The bidirectional model simulates two decoupled inverted pendulums, each restricted to sway in either the anterior-posterior (AP) direction (ankle strategy) or medial-lateral (ML) direction (hip strategy), and each controlled by a Proportional-Integral-Derivative (PID) controller. Postural data was collected from 31 healthy participants under different sensory test conditions: eyes closed, eyes open, and eyes open with real-time visual feedback. Simulation iterations of the bidirectional model were run for each sensory test condition to adjust the PID controller parameters until modeled sway metrics did not differ significantly from experimental metrics at p ≤ 0.01. Simulations did not show significant changes in the AP sway controller parameters among the 3 sensory test conditions. The model did show significant changes in ML sway controller parameters, namely stiffness and time delay. Significant differences were also seen in the experimental sway metrics under the three different sensory test conditions. The multi-sensory evaluation and bidirectional sway model offer unique insight for further exploration of postural pathology, control mechanisms and planar coupling that includes both ankle and hip strategies.

Effect of Lowest Instrumented Vertebra on Trunk Mobility in Patients With Adolescent Idiopathic Scoliosis Undergoing a Posterior Spinal Fusion.

STUDY DESIGN: Prospective. OBJECTIVES: The goal of this study was to evaluate the effect of posterior spinal fusion surgery terminating at different lowest instrumented vertebrae (LIV) on trunk mobility in individuals with adolescent idiopathic scoliosis (AIS). SUMMARY OF BACKGROUND DATA: Posterior spinal fusion with instrumentation is the standard surgical technique employed in AIS for correcting spine deformities with Cobb angles exceeding 50°. Surgical correction of curve deformity reduces trunk mobility and range of motion. However, conflicting findings from previous studies investigating the impact of different LIV levels on the reduction in trunk mobility after surgery have been reported. METHODS: The study was designed as a prospective study with 47 patients (7 males and 40 females) with AIS who underwent posterior spinal fusion. Patients were classified into 5 groups based on their surgical LIV level (ie, T12, L1, L2, L3, and L4). Trunk flexion-extension (sagittal plane), lateral bending (coronal plane), and axial rotation (transverse plane) kinematics were assessed during preoperative, 1 year postoperative, and 2 years postoperative evaluation visits. RESULTS: There were postoperative reductions of 41%, 51%, and 59% in trunk range of motion in the sagittal, coronal, and transverse planes, respectively (p < .0001). A trend toward greater postoperative reductions in peak forward flexion at more distal LIVs was observed (p = .04). CONCLUSIONS: Fusion reduces trunk mobility in the sagittal, coronal, and transverse planes. More distal LIV fusions limit peak forward flexion to a greater extent which is considered clinically significant. After fusion, the reductions seen in axial rotation, lateral bending, and backward extension do not differ significantly at more distal LIVs.

Multiple types of movement-related information encoded in hindlimb/trunk cortex in rats and potentially available for brain-machine interface controls.

Brain-machine interface (BMI) systems hold the potential to return lost functions to patients with motor disorders. To date, most efforts in BMI have concentrated on decoding neural activity from forearm areas of cortex to operate a robotic arm or perform other manipulation tasks. Efforts have neglected the locomotion functions of hindlimb/trunk cortex. However, the role of cortex in hindlimb locomotion of intact rats, which are often model systems for BMI testing, is usually considered to be small. Thus, the quality of representations of locomotion available in this area was uncertain. We designed a new rodent BMI system, and tested decoding of the kinematics of trunk and hindlimbs during locomotion using linear regression. Recordings were made from the motor cortex of the hindlimb/trunk area in rats using arrays of six tetrodes (24 channels total). We found that multiple movement-related variables could be decoded simultaneously during locomotion, ranging from the proximal robot/pelvis attachment point, and the distal toe position, through hindlimb joint angles and limb endpoint in a polar coordinate system. Remarkably, the best reconstructed motion parameters were the more proximal kinematics, which might relate to global task variables. The pelvis motion was significantly better reconstructed than any other motion features.

Robot application of elastic fields to the pelvis of the spinal transected rat: a tool for detailed assessment and rehabilitation.

We examine robotic rehabilitation and assessment of spinalized rats, using robot applied forces at the pelvis, as a prelude to a neurorobotic BMI. Using a surgically implanted pelvic orthosis, a cantilevered phantom robot is attached to the rat pelvis. An isotropic elastic field of constant stiffness is applied and the equilibrium is adjusted to provide a ;natural' trunk posture. Rats are trained daily for 20 minutes, 5 days per week in the field. Significant within trial, and long term adaptation occurs. The interaction force assessments from the robot reveal significant differences between spinalized control rats, and rats receiving implants of E14 dorsal raphe tissue to provide a serotonin source. Our system provides an animal model of rehabilitation through robot interaction at the pelvis.