Effects of noninvasive neuromodulation targeting the spinal cord on early learning of force control by the digits

Aims Control of finger forces underlies our capacity for skilled hand movements acquired during development and reacquired after neurological injury. Learning force control by the digits, therefore, predicates our functional independence. Noninvasive neuromodulation targeting synapses that link corticospinal neurons onto the final common pathway via spike‐timing‐dependent mechanisms can alter distal limb motor output on a transient basis, yet these effects appear subject to individual differences. Here, we investigated how this form of noninvasive neuromodulation interacts with task repetition to influence early learning of force control during precision grip. Methods The unique effects of neuromodulation, task repetition, and neuromodulation coinciding with task repetition were tested in three separate conditions using a within‐subject, cross‐over design (n = 23). Results We found that synchronizing depolarization events within milliseconds of stabilizing precision grip accelerated learning but only after accounting for individual differences through inclusion of subjects who showed upregulated corticospinal excitability at 2 of 3 time points following conditioning stimulation (n = 19). Conclusions Our findings provide insights into how the state of the corticospinal system can be leveraged to drive early motor skill learning, further emphasizing individual differences in the response to noninvasive neuromodulation. We interpret these findings in the context of biological mechanisms underlying the observed effects and implications for emerging therapeutic applications. Sequencing depolorization events in the spinal cord via noninvasive stimulation has been shown to enhance motor output, offering possible therapeutic potential after neurological injury. Our findings show that this neuromodulation strategy enhances learning of force control underlying finger movements but depends on the physiological state of the intact corticospinal system and its responsiveness to neuromodulation.