Eligibility Criteria:
1. Uninjured individuals
Inclusion criteria:
* Ages 18 and up.
* Ability to follow simple commands, and to respond to questions.
Exclusion criteria for SCI participants:
• Does not meet the inclusion criteria.
2. Individuals with SCI
Inclusion criteria:
* Age 16-65
* Injuries at the C3-6 level, complete (ASIA A), or incomplete (ASIA B and C).
* Able to follow simple commands
* Able to speak or respond to questions
Exclusion criteria:
* Presence of tremors, spasm and other significant involuntary movements
* Cognitive impairment
* Deficit of visuo-spatial orientation
* Concurrent pressure sores or urinary tract infection
* Other uncontrolled infection, concurrent cardiovascular disease
* Sitting tolerance less than one hour
* Severe hearing or visual deficiency
* Miss more than six appointments without notification
* Unable to comply with any of the procedures in the protocol
* Unable to provide informed consent
3. Stroke survivors:
Inclusion criteria:
* Recent stroke (Sub acute to early chronic, between 3 and 12 months from CVA)
* Age less than 75 (To avoid age-related confounds)
* Inability to operate a manual wheelchair
* Available medical records and radiographic information about lesion locations
* Significant level of hemiparesis (UE Fugl Meyer score between 10 and 30)
* Presence of pathological muscle synergies in the UE (flexor and/or extensor synergy)
Exclusion criteria:
* Aphasia, apraxia, cognitive impairment or affective dysfunction that would influence the ability to perform the experiment
* Inability to provide informed consent
* Severe spasticity, contracture, shoulder subluxation, or UE pain
* Severe current medical problems, including rheumatoid arthritis or other orthopaedic impairments restricting finger or wrist movement
Additional exclusion criteria for participants enrolled in TMS procedures
* Any metal in head with the exception of dental work or any ferromagnetic metal elsewhere in the body. This applies to all metallic hardware such as cochlear implants, or an Internal Pulse Generator or medication pumps, implanted brain electrodes, and peacemaker.
* Personal history of epilepsy (untreated with one or a few past episodes), or treated patients
* Vascular, traumatic, tumoral, infectious, or metabolic lesion of the brain, even without history of seizure, and without anticonvulsant medication
* Administration of drugs that potentially lower seizure threshold \[REF\], without concomitant administration of anticonvulsant drugs which potentially protect against seizures occurrence
* Change in dosage for neuro-active medications (Baclophen, Lyrica, Celebrex, Cymbalta, Gabapentin, Naprosyn, Diclofenac, Diazepam, Tramadol, etc) within 2 weeks of any study visit.
* Skull fractures, skull deficits or concussion within the last 6 months
* unexplained recurring headaches
* Sleep deprivation, alcoholism
* Claustrophobia precluding MRI
* Pregnancy