Temporary Inactivation of Strong Muscle Sensation to Improve Rehabilitation Interventions in SCI

The investigators are conducting a research study to try to improve rehabilitation interventions for individuals with spinal cord injury (SCI). In this study, the aim is to determine if temporarily numbing non-paralyzed arm muscles with an over-the-counter numbing cream while exercising paralyzed muscles, can improve the strength, function, and sensation of paralyzed muscles after a spinal cord injury.

The functional benefits of temporary deafferentation (numbing)-induced cortical plasticity have been demonstrated in individuals with stroke, nerve damage, and pain syndromes. Of note, documented benefits have included improvements in motor function and touch perception in the weaker muscles. For example, Weiss et al demonstrated that temporary deafferentation to the forearm of the paretic limb in stroke for two hours during movement therapy improved motor performance of the hand by 10 to 48% after a single session. Another study established that bi-weekly sessions of temporary deafferentation for two weeks improved two-point discrimination and touch perception in individuals with ulnar/median nerve damage. More importantly, the authors found that improvements were retained for more than four weeks after the intervention ended. Collectively, this suggests that the release of tonic inhibition on weak muscle pathways, through temporary deafferentation, can lead to functional benefits that are retained long-term.

The Investigators' pilot findings indicate that temporary deafferentation shows similar benefits in the population of SCI. Specifically, it was observed that a single 30-minute session of temporary deafferentation to the stronger biceps can improve excitability to the weaker triceps and result in gains in hand dexterity and pinch strength in SCI.

The Investigators now seek to optimize the current study protocol before a large-scale clinical trial is conducted.

Eligibility Criteria:
Inclusion Criteria:

SCI Patients:

* Provision of signed and dated informed consent form
* Stated willingness to comply with all study procedures and availability for the duration of the study
* Male or female, aged between 18 and 75 years old
* Have physician diagnosed cervical incomplete spinal cord injury or lesion (iSCI)
* Classified by the American Spinal Cord Association (AIS) impairment scale as AIS C or D
* iSCI occurred at least 18 months ago
* Level of injury or lesion is between C2 and T1
* Bicep strength must be classified as ≥ 3 muscle grade as defined by the medical research council scale
* Tricep strength must be at least an MRC grade of 2 and bet at least 1 muscle grade lower than the bicep
* Both the biceps and triceps will be required to elicit an active motor evoked potential \>200 uV with transcranial magnetic stimulation
* Must maintain current medication regime
* Must present with a weaker side of the body, as indicated by a Upper extremity motor score difference between the left and right side
* UEMS \< 40 (50 max score)
* Must be able to perform reaching movement training task

Healthy Controls:

* Provision of signed and dated informed consent form
* Stated willingness to comply with all study procedures and availability for the duration of the study
* Male or female, aged between 18 and 75 years old
* Must be right-handed
* Must be able to perform hand exercises

Exclusion Criteria:

SCI Patients:

* Pacemaker or another implanted device
* Metal in the skull
* History of seizures
* Pregnancy
* First-degree relative with medication-resistant epilepsy
* Current participation in upper limb rehabilitation therapies
* Current use of illicit drugs, abusing alcohol, or have withdrawn from alcohol in the last 6 months
* Other neurological impairment or condition
* Pressure ulcers
* Significant lower motor neuron loss at C7 as noted by a nerve conduction velocity \<50 m/s
* History of traumatic brain injury as documented by Rancho Scale Impairment of \<5
* History of brain MRI documented focal cerebral cortex infarct (e.g. hydrocephalus)
* Contractures at the elbow
* Severe spasticity as noted by a modified ashworth scale (MAS) \> 4
* Documented, non-sedated post-traumatic amnesia lasting more than 48 hours
* Pregnancy
* Allergic to lidocaine
* A neuroactive medication that has the potential to lower the seizure threshold

  * Based on documented publications in stroke, this will include bupropion (wellbutrin), psychostimulants and neuroleptics
  * All medications will be reviewed with physician, Dr. Amol Utturkar (DHR)

Healthy Controls:

* Pacemaker or other implanted device
* Metal in the skull
* History of seizures
* First-degree relative with medication-resistant epilepsy
* Current use of illicit drugs (including heroin, crack/cocaine, marijuana), abusing alcohol or having withdrawn from alcohol in the last 6 months
* Allergy to lidocaine
* Other neurological impairment or condition
* Pregnancy
* A neuroactive medication that has the potential to lower the seizure threshold
* Based on documented publications on stroke, this will include bupropion (wellbutrin), psychostimulants and neuroleptics