Spinal Cord Associative Plasticity in Cerebral Palsy

Associative plasticity has been used to promote functional recovery in patient populations, such as adults with spinal cord injuries (SCI). Using safe and well-tolerated non-invasive neuromodulation approaches, pairing of motor cortical stimulation and peripheral nerve stimulation has been shown to augment motor responses and promote plasticity, primarily through the convergence of sensory afferent stimuli and descending cortical stimuli in the motor cortex.

Our laboratory has shown that paired associative stimulation timed to converge in the cervical spinal cord induces significantly larger upper limb motor responses than if timed to converge in the motor cortex. While paired associative stimulation has shown promise for strengthening motor responses, it is unclear if plasticity from convergence of non-invasive stimuli in the spinal cord (termed spinal cord associative plasticity or SCAP) instead of the motor cortex can produce greater motor effects, and potentially greater promotion of movement recovery.

The goal of this present study is to test the effects of pairing sub-threshold hand motor cortical and median nerve stimulation targeted to induce plasticity in the cervical spinal cord of adults with hemiplegic cerebral palsy. The investigators aim to fill a knowledge gap regarding the ideal target of non-invasive stimulation to maximize associative plasticity for upper limb movement recovery. The study hypothesis is that pairing stimulation of the hand motor cortex with median nerve stimulation will produce associative plasticity in the cervical spinal cord measured through augmentation of motor responses in upper limb muscles, leading to improvements in dexterity.

This study will first verify that the present stimulation parameters are sufficient to promote induction of associative plasticity of sensorimotor connections for manual dexterity. The outcomes from this study could be translated to an efficacy study in people with CP to test whether pairing brain and afferent-targeted nerve stimulation for convergence in the cervical spinal cord can lead to clinically meaningful improvements in manual dexterity.

Inclusion criteria

• Maintenance of caffeine and exercise levels at time of sessions
• Ability to provide informed consent
• Manual ability classification system (MACS) level I to III

Exclusion criteria

• History of seizures in last two years
• Use of medications that lower seizure threshold
• History of implanted equipment including stimulators/pacemakers