Spinal Cord Associative Plasticity for ALS

Inclusion Criteria: * Diagnosis of ALS by Gold Coast Criteria (Shefner et al. 2020) or "definite" or "probable" ALS by revised El Escorial Criteria (Brooks et al. 2000) * Incomplete weakness: Score of 1, 2, 3, or 4 (out of 5) on manual muscle testing of finger extension, finger flexion, or finger abduction in left or right hand * TSCS-evoked potential amplitude of at least 25 V in left or right abductor pollicis brevis (APB) or first dorsal interosseous (FDI) muscles with a resting motor threshold of 55 mA or lower * TMS-evoked potential amplitude of at least 25 V in left or right abductor pollicis brevis (APB) or first dorsal interosseous (FDI) muscles with a resting motor threshold of 65% MSO or lower Exclusion Criteria: * History of seizures * Ventilator dependence or patent tracheostomy site * Use of medications that significantly lower seizure threshold, such as amphetamines and dalfampridine * History of severe head trauma (evidence of brain contusion or hemorrhage or depressed skull fracture on prior imaging) * History of implanted brain/spine/nerve stimulators, aneurysm clips, ferromagnetic metallic implants in the head (except for inside mouth); cochlear implants; cardiac pacemaker/defibrillator; intracardiac lines; currently increased intracranial pressure; or other contraindications to brain or spine stimulation * Significant coronary artery or cardiac conduction disease; heart failure with an ejection fraction of less than 30% or with a New York Heart Association Functional Classification of Class III or IV * History of significant tinnitus * History of bipolar disorder * History of suicide attempt * Active psychosis * Ongoing illicit drug or alcohol abuse in the past 6 months * Heavy alcohol consumption (greater than equivalent of 5 ounces of liquor) within previous 48 hours * Open skin lesions over the neck, shoulders, or arm stimulation or recording sites * Pregnancy