Bimanual upper limb task practice and Transcutaneous electrical stimulation enhance spinal plasticity and hand function after chronic cervical spinal cord injury

Injuries to the spinal cord at the cervical level can lead to loss of upper limb function. Recent work suggests that combining functional task practice with Transcutaneous electrical stimulation of the spinal cord (TCES) can increase strength and upper limb function in people living with chronic cervical spinal cord injury (cSCI). Participants ( n = 5) were randomly assigned to: Group_1 ( n = 3) receiving one month of upper limb task practice (ULTP) followed by one month of upper limb task practice paired with spinal stimulation (ULTP+TCES); Group_2 ( n = 2) receiving one month of ULTP+TCES followed by one month of ULTP. Changes in hand function (assessed via the Graded Redefined Assessment of Strength, Sensibility), independence and quality of life were investigated after each intervention and at three-months follow-up. In addition, we assessed cortical (via Transcranial Magnetic Stimulation) and spinal (via single-pulse TCES) excitability at those same time points. For Group_1: improvements in hand function from baseline were observed after ULTP+TCES ( p< 0.001) and at follow-up ( p= 0.017); quality of life increased between baseline and after ULTP ( p= 0.002), ULTP+TCES ( p< 0.001) and at follow-up ( p= 0.013); spinal excitability increased from baseline to after ULTP+TCES ( p <0.001). For Group_2: improvements in hand function from baseline were observed after ULTP+TCES ( p< 0.001), ULTP ( p< 0.001) and at follow-up ( p< 0.001); corticospinal excitability increased from baseline to after ULTP ( p =0.013); spinal excitability increased from baseline to after ULTP+TCES ( p <0.001) and the increase persisted 3 months later at follow-up ( p =0.04). Our findings demonstrate that non-invasive spinal stimulation paired with task practice can improve hand function more than task practice alone in people living with a cSCI. In addition, we suggest that spinal plasticity induced by spinal stimulation is a potential neural substrate for the attained improvements in hand function.