The purpose of this study is to investigate neuromodulation as new approach to enhance rehabilitation for people who have upper limb movement impairment after neurological injury such as stroke or spinal cord injury. Emerging evidence demonstrates that animals and people can exert control over the level of excitability in neural pathways that contribute to movement. This discovery has important implications, as it represents a new strategy to improve motor control in people of all ability levels, including those with neurological conditions. Operant conditioning is a well-studied mechanism of learning, in which the modification of a behavior can be brought about by the consequence of the behavior. Behaviors that are rewarded with positive reinforcement are displayed more frequently. In recent years, operant conditioning has been applied to spinal reflex responses in mice, rats, monkeys and people. Evidence suggests that it is possible to increase or decrease a neural circuit's excitability, by electrically stimulating a nerve or an area of the brain, then recording the muscle response and rewarding responses that are within a desirable range. This may alter the level of resting muscle tone, as well the muscle's contribution to intentional movements and its readiness to respond to unexpected perturbations. To date, only one research group has applied operant conditioning to improve motor performance in people. Their work has focused on modifying spinal reflexes for a lower limb muscle and the effects on walking. In the proposed project, we will expand the use of operant conditioning to muscles of the upper limb and to people with movement impairment following stroke and spinal cord injury, and to another neural pathway in addition to the spinal reflex.

This study will include procedures necessary to measure excitability of the nervous system at the level of the spinal cord and at the level of the brain. Spinal reflex excitability will be quantified by electrically stimulating a peripheral nerve and recording the muscle response (ie. the H-reflex) with electromyography. Excitability of the motor pathway from brain to muscle (the corticospinal tract) will be quantified by stimulating a specific area of the brain (the motor cortex) with transcranial magnetic stimulation, and recording the muscle response (ie. The motor evoked potential) with electromyography. In addition, upper limb movement impairment will be assessed by measuring muscle tone, sensation, ability to generate force, and performance on a computer-based wrist motor control task. In subjects who have neurological conditions, upper limb function will be assessed using standardized tests, including the Fugl-Meyer a assessment of the Upper Extremity, the Action Research Arm Test, and the Box and Blocks Test. This study will test the effectiveness of operant conditioning as an intervention to modify neural excitability. After baseline testing, subjects will participate in up to 12 sessions of sham intervention followed by up to 24 sessions of real operant conditioning intervention. Each session will include 225 trials (3 sets of 75), lasting about 30 minutes. For each trial during real intervention, a stimulus will be delivered while the subject maintains a low level muscle contraction, the muscle's response to stimulation will be recorded, and immediate feedback will be displayed on a computer screen, showing the subject whether their muscle response was within the desired range or not. For example, a green bar will appear if the muscle response was 'good', otherwise a red bar will appear. The subject's 'percent success' also will be displayed and updated after each trial. During sham intervention, all procedures will be identical except that no feedback will be provided to the subject, and there will be no instructions to either increase or decrease their muscle responses.

In healthy people, we will aim to shift spinal reflex excitability (H-reflexes) of an upper extremity muscle either upward or downward, expanding on previous findings showing those effects in a lower limb muscle, with no effect on normal movement ability (Thompson et al., 2009, Makihara et al., 2014). Also in healthy people, we will aim to shift excitability of the pathway from brain to muscle either upward or downward, using operant conditioning of motor evoked potentials. Only one prior study (Majid et al., 2015) has demonstrated a downward shift, and the first studies investigating the ability to increase motor evoked potentials currently are in progress. People with neurological conditions often have abnormally increased spinal reflex excitability affecting certain muscles, resulting in increased tone, stiffness, and difficulty moving. Therefore, we will aim to reduce spinal reflex excitability in over-active muscles, by eliciting H-reflexes and rewarding responses that are below a threshold. In addition, people with neurological conditions often have disrupted connections from brain to muscle, resulting in weakness (diminished ability to generate force). Therefore, we will aim to increase excitability of the pathway from brain to muscle, by eliciting motor evoked potentials and rewarding responses that are above a threshold.