Interhemispheric Connectivity and Compensation

This study contains two groups: typical controls and patients. Participants will be matched by age and sex between the two groups. No randomization will occur. A. Inclusion criteria (all participants): 1. Age ≥ 18 2. English speaking and reading 3. Able to fit in Prisma scanner bore (60 cm diameter) 4. Right hand dominant (self report, and Edinburgh handedness ≥ +40) B. Inclusion criteria (patients only): 1. Chronic unilateral upper extremity peripheral nerve injury to the right side * "Chronic" defined as ≥ 6 months since injury * "Upper extremity" defined as hand, arm, or shoulder (including e.g. brachial plexus) * "Injury" defined as localized cause (e.g. mechanical/tumor, not distributed pathology), including compression 2. Some impairment to writing, requiring both of: * Difficulty writing, as determined by score 2+ (Mild+) on "How much difficulty have you had in the last week with writing?" (From Disabilities of the Arm, Shoulder, and Hand survey question #2) * Box and Blocks motor performance ≥1 standard deviation below the mean of age-matched healthy adults (Mathiowetz et al. 1985, AJOT). C. Exclusion criteria (all participants) 1. Currently intoxicated or otherwise non-compliant 2. Chronic pain diagnosis unrelated to the nerve injury 3. Uncorrected visual impairment that interferes with ability to see drawings in MRI 4. Motor function diagnoses that affect function of the left hand, now or in past 2 years 5. Motor function diagnoses currently affecting the right hand, unrelated to the nerve injury * This is not meant to exclude a single event with complex consequences (e.g. nerve and tendon) * This is not meant to exclude multiple nerve injuries in the same arm, if each one is eligible (II.B.1) * This is meant to exclude e.g. injury and unrelated musculoskeletal disorder in same arm 6. Upper extremity surgery, including peripheral nerve surgery, within last 2 months 7. Contraindication for MRI 8. Contraindication for transcranial magnetic stimulation (TMS) * May exclude from TMS only (since not all participants undergo TMS), or exclude from full study 9. Amputation affecting any part of thumb, index, or middle fingers (including higher level, e.g. whole hand) 10. History of chronic cocaine use (based on medical record or volunteered; will not actively inquire) 11. Diagnosis of schizophrenia or other rare psychiatric disorder * This is not meant to exclude depression or anxiety 12. History of major neurological diagnosis, e.g. stroke, traumatic brain injury, Alzheimer's, Parkinson's * This is not meant to exclude concussion UNLESS \< 6 months ago, or post-concussion syndrome (diagnosed or self-report) D. Exclusion criteria (controls only) 1\. Motor function diagnoses that affect function of either hand, now or in past 2 years