Spinal cord injury (SCI) and amyotrophic lateral sclerosis (ALS) result in a mixture of destroyed, damaged, and spared neural circuits. Activating spared nerve circuits augments neural transmission.~With this goal in mind, the investigators recently developed a novel method of cervical electrical stimulation (CES) to noninvasively activate arm and hand muscles. The investigators are conducting a pilot clinical study (NCT02469675) to establish CES safety in subjects with cervical SCI, ALS, and non-disabled volunteers. To date, 19 subjects have undergone >120 CES sessions without major safety or tolerability issues.~The current study is designed to gain further mechanistic insight. In Aim 1, the investigators will test in more detail how CES (traveling through spinal and peripheral circuits) interacts with individual pulses of TMS (traveling through corticospinal circuits). In Aim 2, the investigators will further test CES's therapeutic potential by combining stimulation with simultaneous physical exercises. In Aim 3, the investigators will compare the acute effects on synaptic transmission of passive stimulation to stimulation triggered by the subject's own muscle activity.~Please note, this is a preliminary study. This study is testing for temporary changes in nerve transmission to hand muscles. There is no expectation of long-term benefit from this study. If the investigators see temporary changes in this study, then future studies would focus on how to prolong that effect.
People with cervical spinal cord injury (SCI) and amyotrophic lateral sclerosis (ALS) have reduced connections in the nerve circuits between the brain and the hands. Activating spared nerve circuits is one potential way to improve recovery.~The investigators are testing different combinations of physical wrist and hand movements paired with magnetic brain stimulation and electrical spinal cord or nerve stimulation to see the effects on nerve transmission to hand muscles.~This is a preliminary study. This study is testing for temporary changes in nerve transmission to hand muscles. There is no expectation of long-term benefit from this study. If temporary changes are seen in this study, then future studies would focus on how to prolong that effect.