Operant Conditioning for Neuromodulation

Emerging evidence demonstrates that animals and people can exert control over the level of
excitability in spinal and corticospinal neural circuits 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, and reinforcement causes
behaviors to become more frequent. In recent years, operant conditioning has been applied to
spinally-mediated reflex responses in mice, rats, monkeys and people. By electrically
stimulating a peripheral nerve, recording the muscle response, and rewarding responses that
are within a desirable range, it is possible to increase or decrease the neural circuit's
excitability. This may alter the level of resting muscle tone and spasticity, as well the
muscle's contribution to planned movements and responses to unexpected events. Operant
conditioning of spinal reflexes has been applied to a lower limb muscle in healthy people and
those with spinal cord injuries. In this project, we will expand the use of operant
conditioning to muscles of the upper limb, demonstrating feasibility and efficacy in healthy
people and people post-stroke. We will determine whether operant conditioning can be used to
decrease excitability of spinal reflexes that activate a wrist flexor muscle. Additionally,
in a separate group of healthy people, we will determine whether operant conditioning can be
used in a similar way to increase corticospinal excitability. We will stimulate the motor
cortex with transcranial magnetic stimulation to elicit motor evoked potentials in the same
wrist flexor muscle, and will reward responses that exceed a threshold value. We will examine
the effects of these interventions on motor control at the wrist, using an innovative
custom-designed cursor-tracking task to quantify movement performance. We will determine
whether changes in spinal reflex excitability or corticospinal excitability alter motor
control. The overall goal of this research is to develop a new, evidence-based strategy for
rehabilitation that will improve recovery of upper limb function in people after stroke.