Corticospinal inhibition investigated in relation to upper extremity motor function in cervical spinal cord injury

Abstract

Objective: Corticospinal inhibitory mechanisms are relevant to functional recovery but remain poorly understood after spinal cord injury (SCI). Post-injury characteristics of contralateral silent period (CSP), a measure of corticospinal inhibition evaluated using transcranial magnetic stimulation (TMS), is inconsistent in literature. We envisioned that investigating CSP across muscles with varying degrees of weakness may be a reasonable approach to resolve inconsistencies and elucidate the relevance of corticospinal inhibition for upper extremity function following SCI.

Methods: We studied 27 adults with chronic C1-C8 SCI (age 48.8 ± 16.1 years, 3 females) and 16 able-bodied participants (age 33.2 ± 11.8 years, 9 females). CSP characteristics were assessed across biceps (muscle power = 3-5) and triceps (muscle power = 1-3) representing stronger and weaker muscles, respectively. We assessed functional abilities using the Capabilities of the Upper Extremity Test (CUE-T).

Results: Participants with chronic SCI had prolonged CSPs for biceps but delayed and diminished CSPs for triceps compared to able-bodied participants. Early-onset CSPs for biceps and longer, deeper CSPs for triceps correlated with better CUE-T scores.

Conclusions: Corticospinal inhibition is pronounced for stronger biceps but diminished for weaker triceps muscle in SCI indicating innervation relative to the level of injury matters in the study of CSP.

Significance: Nevertheless, corticospinal inhibition or CSP holds relevance for upper extremity function following SCI.

Keywords: Electrophysiology; Functional recovery; Neurological assessment; Neurophysiology; Neurorehabilitation; Tetraplegia.