Task-related brain activity is altered by the frequency of transcutaneous spinal stimulation

Abstract

Transcutaneous spinal stimulation (TSS) has been used to restore voluntary motor function in individuals with spinal cord injury. It was previously suggested that exposure to different frequencies of TSS could promote the recovery of motor functions in a task-specific way. Exposure of higher frequencies (e.g., 30Hz) of stimulation was shown to promote the recovery of locomotion whereas exposure to lower frequencies (e.g. 15Hz) of stimulation was shown to promote the recovery of postural control. It remains unknown however, if exposure to these different TSS frequencies leads to task- specific functional activation in sub-cortical and cortical networks. To examine the ascending effects of TSS on brain activation patterns, 7 healthy participants were exposed to TSS at two different frequencies (15Hz, and 30Hz) while at rest and while attempting to perform constrained motor tasks (standing and stepping). Brain activation was assessed using functional magnetic resonance imaging (fMRI). Overall, exposure to 15Hz TSS resulted in significant increases in activation during standing and exposure to 30Hz stimulation resulted in significant increases in activation during stepping. TSS- induced facilitation was localized to areas of the sensorimotor network (e.g. posterior parietal and motor cortex) and other brain areas involved in balance control and locomotion (e.g., cerebellum and brainstem). These results provide evidence that altering TSS parameters selectively engages brain areas associated with task performance.