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

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.

Gender differences in ergonomics during simulated ureteroscopy.

BACKGROUND: Female urologists report higher rates of work-related physical discomfort compared to male urologists. We compared ergonomics during simulated ureteroscopy, the most common surgery for kidney stones, between male and female urologists. METHODS: Surface electromyography was used to measure muscle activation during common ureteroscopic tasks in urology trainees and staff with different surgeon positions and ureteroscopes. Subjective workload was assessed using the NASA Task Load Index (NASA-TLX). Paired t-tests, Wilcoxon rank-sum tests, and multivariate regressions were used to compare muscle activation by gender for each trial condition. RESULTS: There was no difference in age or distribution of training level between genders, though men had larger glove sizes. Across all conditions, women required greater muscle activation in multiple muscle groups and had greater NASA-TLX scores compared to men. CONCLUSIONS: There may be gender differences in ergonomics during ureteroscopy based on muscle activation and subjective workload, suggesting potential for personalizing surgical ecosystems.

Paired DBS and TMS Reveals Dentato-Cortical Facilitation Underlying Upper Extremity Movement in Chronic Stroke Survivors.

BACKGROUND: Cerebellum shares robust di-synaptic dentato-thalamo-cortical (DTC) connections with the contralateral motor cortex. Preclinical studies have shown that DTC are excitatory in nature. Structural integrity of DTC is associated with better upper extremity (UE) motor function in people with stroke, indicating DTC are important for cerebellar influences on movement. However, there is a lack of understanding of physiologic influence of DTC in humans, largely due to difficulty in accessing the dentate nucleus. OBJECTIVE: Characterize DTC physiology using dentate nucleus deep brain stimulation (DBS) combined with transcranial magnetic stimulation (TMS) in stroke. METHODS: Nine chronic stroke survivors with moderate-to-severe UE impairment (Fugl-Meyer 13-38) underwent a paired DBS-TMS experiment before receiving experimental dentate nucleus DBS in our first-in-human phase I trial (Baker et al., 2023, Nature Medicine). Conditioning DBS pulses were given to dentate nucleus 1 to 10 ms prior to supra-threshold TMS pulses given to ipsilesional motor cortex. Effects were assessed on motor evoked potentials (MEPs). Size of DBS-conditioned MEPs was expressed relative to TMS MEPs, where values >1 indicate facilitation. RESULTS: Dentate nucleus DBS led to facilitation of MEPs at short-latency intervals (3.5 and 5 ms, P = .049 and .021, respectively), a phenomenon we have termed dentato-cortical facilitation (DCF). Higher DCF was observed among patients with more severe UE impairment. Diffusion tensor imaging revealed microstructure of thalamo-cortical portion of DTC was related to higher corticomotor excitability. CONCLUSIONS: Our in vivo investigation reveals for the first time in humans the intrinsic excitatory properties of DTC, which can serve as a novel therapeutic target for post-stroke motor recovery.