Influence of Transcranial Electrical Stimulation on Arm and Hand Function After Cervical Spinal Cord Injury

Participants will participate in a single session of each of the three tES types being evaluated combined with upper extremity FTP.

tDCS (waveform: monophasic and continuous) will be delivered for a duration of 20 minutes and intensity of 2 mA using two saline-soaked reusable sponge electrodes (35 cm2 each). The active electrode will be placed over the hand representation of the motor cortex controlling the right upper extremity (C3, 10-20 EEG system) and the reference electrode will be placed over the contralateral supraorbital area (FP2, 10-20 EEG system). The FTP component of intervention will occur concurrently with tDCS application and will consist primarily of task-oriented arm and hand activities.

tPCS (waveform: monophasic square waves with 500 ms pulse duration and 50 ms inter-pulse interval) will be delivered for a duration of 20 minutes and intensity of 2 mA using two saline-soaked reusable sponge electrodes (35 cm2 each). The active electrode will be placed over the hand representation of the motor cortex controlling the right upper extremity (C3, 10-20 EEG system) and the reference electrode will be placed over the contralateral supraorbital area (FP2, 10-20 EEG system). The FTP component of intervention will occur concurrently with tPCS application and will consist primarily of task-oriented arm and hand activities.

tRNS (waveform: 0-500 Hz random frequency and Gaussian white noise random intensity) will be delivered for a duration of 20 minutes and intensity range of +/-1 mA using two saline-soaked reusable sponge electrodes (35 cm2 each). The active electrode will be placed over the hand representation of the motor cortex controlling the right upper extremity (C3, 10-20 EEG system) and the reference electrode will be placed over the contralateral supraorbital area (FP2, 10-20 EEG system). The FTP component of intervention will occur concurrently with tRNS application and will consist primarily of task-oriented arm and hand activities.

Participants will participate in a single session of sham tES combined with upper extremity FTP.

Sham tES will be delivered for a duration of 20 minutes and intensity of 0 mA using two saline-soaked reusable sponge electrodes (35 cm2 each). The active electrode will be placed over the hand representation of the motor cortex controlling the right upper extremity (C3, 10-20 EEG system) and the reference electrode will be placed over the contralateral supraorbital area (FP2, 10-20 EEG system). The FTP component of intervention will occur concurrently with sham tESapplication and will consist primarily of task-oriented arm and hand activities.

Electroencephalography (EEG) event-related potential (ERP) amplitude will be recorded in the left parietofrontal network during performance of a modified serial reaction time task (mSRTT).

Electroencephalography (EEG) alpha band parietofrontal connectivity will be recorded under two conditions: 1) resting state and 2) during performance of a modified serial reaction time task (mSRTT).

Function will be measured in the right UE using the Graded Redefined Assessment of Strength Sensibility and Prehension version 2 (GRASSP v2) quantitative prehension subtest. Participants will complete four tasks: pouring water from a bottle to a cup, moving nine pegs from one side of a board to the other, inserting a key into a lock and rotating, and fastening four nuts onto screws. Each task will be scored on a 0-5 scale (0: task cannot be conducted at all - 5: task conducted without difficulty using the expected grasp pattern) and timed (maximum of 75 seconds will be allowed per task). The number of drops during each task will also be recorded. The total score, time and number of drops for all four tasks will then be calculated. The maximum score is 20 with higher scores denoting better UE function.

Strength will be measured in the right UE using key pinch force. The participant will be positioned with the shoulder in neutral, elbow flexed at approximately 90º, and forearm and wrist in neutral. Force will be quantified with an electronic pinchmeter positioned between the middle phalanx of the index finger and thumb pad. The participant will be given a command of "ready, set, go" upon which they will be instructed to pinch as hard as possible for 3 seconds. Three trials will be completed with a 60 second rest period between trials, and the mean force will be calculated.

Sensation will be measured in the right UE using the Graded Redefined Assessment of Strength Sensibility and Prehension version 2 (GRASSP v2) sensation subtest. Semmes-Weinstein monofilaments ranging in size from 3.61 to 6.65 will be used in three locations on the palmar surface of the hand while the participant's vision is occluded with a blindfold. The smallest monofilament (3.61) will be tested 3 times per location with 2/3 accurate responses indicating intact sensation. If the participant cannot detect the 3.61 filament at all locations, testing will continue with the next heaviest filament until the participant detects a filament at all three test locations or until testing with the heaviest filament is complete. In contrast to the 3.61 filament, the three other filaments will be tested once per location. The total score will be calculated by summing the scores for each test location. The maximum score is 12 with higher scores denoting better UE sensation.