Characteristics of the Cortical Silent Period in Individuals with and without Spinal Cord Injury

Objective To increase our knowledge of corticospinal excitability changes in persons with spinal cord injury (SCI) by comparing the cortical silent periods (CSPs) of persons with chronic, incomplete cervical SCI to the CSPs of able‐bodied (AB) volunteers. Methods The CSP is a corticospinal inhibitory response (1). It appears as gap in electromyographic (EMG) activity of a voluntarily contracting muscle due to transcranial magnetic stimulation (TMS) delivered to the motor cortex (see Figure A). We measured TMS‐induced CSPs in 5 participants with chronic, incomplete cervical SCI and 5 AB volunteers as an exploratory outcome of a larger study assessing the effects of non‐invasive stimulation in persons with and without SCI. EMG data was collected from the abductor pollicis brevis muscle of the dominant hand in each subject. We recorded a total of 139 CSPs in the SCI participants and 176 in the AB participants. Further analysis of 4 more SCI subjects and 10 more AB subjects is ongoing. Results The preliminary results suggest that the average CSP duration of the SCI group (89 ± 34 ms) was less than that of the AB group (116 ± 30 ms). While statistically insignificant, (p = 0.230; Figure B), our results corroborate previous findings of shortened CSPs in persons with SCI (2). Moreover, the proportion of CSPs with at least one “interruption,” visualized as a momentary spike in EMG activity lasting 5–10 ms (see Figure C), was higher in the SCI group (14.48% of CSPs) than in the AB group (2.56% of CSPs; ns; Figure D). Conclusions Our preliminary findings, of shorter CSP duration and higher frequency of CSP interruptions in subjects with SCI, may imply that cortical inhibitory pathways are damaged or less excitable in persons with SCI. CSP parameters may be valuable outcome measures in the study of SCI. Support or Funding Information New York Spinal Cord Injury Research Board (DOH01‐CARTID‐2015‐00037) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .