The purpose of this study is to establish the value of combined non-invasive stimulation (tDCS) and behavioral training (robotics) in SCI rehabilitation, and understand the mechanisms of this interaction and its relationship to functional outcome. The investigators hypothesize that supplementary tDCS will augment the functional improvement from robot-training, in chronic SCI.

Study design: Using a within-subjects repeated measures design, up to 40 SCI participants will be randomized to receive 6-week hand robotic training preceded by 20 min anodal 2mA tDCS or sham (3 sessions/week, 18 sessions total). Clinical and functional scales, robotic kinematics and neurophysiological data (TMS evaluation) will be collected before and after the combined intervention period, and a month later (pre, post and follow up evaluations). Randomization will be done using a randomized block design with a block size of 2. All participants, raters, and experimenters will be blinded to treatment allocation.

AIM 1. To determine whether combining non-invasive brain stimulation (tDCS) and behavioral training (robotics) in SCI can lead to functional improvement. The investigators hypothesize that the group receiving the real stimulation will obtain a greater clinical improvement in hand motor function. Using a within subjects repeated measures design, baseline clinical hand function (Box and Blocks test) will be compared to post 6-week robotic training intervention, and then a month later (follow up), each session preceded by real (2mA anodal M1) or sham tDCS.

AIM 2. To examine the kinematic changes (from robotic measures) associated with the combined training. Quantitative measurements obtained from robotics are highly sensitive, precise and reliable. The investigators predict an enhancement of motor performance in all participants, measured by 5 key parameters: mean speed, peak speed, smoothness, aim and deviation; with greater improvements in the intervention group receiving the pre-conditioning effect of transcranial stimulation. These data will identify features of motor control that underlie improvements in clinical function, when comparing the two intervention groups.

AIM 3. To identify and compare the neurophysiological mechanisms (by TMS) associated with the combined training. The relationship between clinical improvement in neurophysiological measures pertaining to robotic motor training alone and combined with tDCS will be assessed. Measuring changes in MEP amplitude of hand muscles before and after the training will establish a) the plasticity associated with training alone and with supplementary brain stimulation, b) the neurophysiological characteristics of patients who respond better to the training. By understanding how brain excitability changes underpin motor dysfunction, and motor recovery, interventions can be more effectively prescribed and prognoses established.

Inclusion Criteria:

• Tetraplegia (cervical lesion) with some degree of motor dysfunction in the hand (ability to pick up at least 1 block on the Box and Blocks Test)
• Motor incomplete lesion (measured by the ASIA Impairment Scale, B, C, D)
• Chronic lesion (>6 months after the injury)

Exclusion Criteria:

• Motor and sensory complete lesion (AIS A)
• Presence of potential risk factor for brain stimulation (TMS and tDCS): history of seizures, presence of surgically implanted foreign bodies such as a pacemaker, metal plate in the skull, and metal inside the skull
• History of head trauma and/or cognitive deficit
• Medically unstable

There is no plan to make individual participant data available to other researchers at this time.

All participants, raters, and experimenters will be blinded to treatment allocation.