Establishing between-session reliability of TMS-conditioned soleus H-reflexes

Abstract

Transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) can be used to evaluate descending corticomotor influences on spinal reflex excitability through modulation of the Hoffman reflex (H-reflex). The purpose of this study was to characterize between-session reliability of cortical, spinal, and cortical-conditioned spinal excitability measures collected from the soleus muscle. Thirteen able-bodied young adult participants were tested over four sessions. Intraclass correlation coefficients were calculated to quantify between-session reliability of active motor threshold (AMT), unconditioned H-reflexes (expressed as a percentage of Mmax), and conditioned H-reflexes using short-latency facilitation (SLF) and long-latency facilitation (LLF). Pearson correlation coefficients were calculated to assess associations between H-reflex facilitation and unconditioned H-reflex amplitude. Between-session reliability for SLF (ICC = .71) was higher than for LLF (ICC = .45), was excellent for AMT (ICC = .95), and was moderate for unconditioned H-reflexes (ICC = .63). Our results suggest moderate-to-good reliability of SLF and LLF to evaluate cortical influences on spinal reflex excitability across multiple testing sessions in able-bodied individuals.

The use of transcranial magnetic stimulation to evaluate cortical excitability of lower limb musculature: Challenges and opportunities

“…For example, pairing TMS with peripheral nerve stimulation at varying latencies can elucidate how descending circuits influence the spinally-mediated Hoffman’s reflex (H-reflex) response. TMS-conditioning of the H-reflex has been used to evaluate short-latency facilitation (SLF) and long-latency facilitation (LLF) (Geertsen, van de Ruit, Grey, & Nielsen, 2011; Gray, Sabatier, Kesar, & Borich, 2017). SLF is purported to reflect the strength of fast-conducting monosynaptic descending projections, while LLF evaluates the strength of the indirect, polysynaptic descending projections (e.g.…”

“…SLF is purported to reflect the strength of fast-conducting monosynaptic descending projections, while LLF evaluates the strength of the indirect, polysynaptic descending projections (e.g. cortico-reticular, cortico-vestibular) onto the lower motor neuron pool (Geertsen et al, 2011; Gray, Sabatier, et al, 2017). Given the potentially greater role played by polysynaptic descending pathways in LE motor control, measures such as LLF may be particularly valuable for LE studies.…”

Characterizing the corticomotor connectivity of the bilateral ankle muscles during rest and isometric contraction in healthy adults

“…Additionally, the study’s results for MEP amplitude showed high ICC and relatively high typical percentage error, similar to our results. The second study examined only active motor threshold of the right SOL, which had an ICC of 0.95 (Gray, Sabatier, 2017). Though SOL CSP was feasibly measured in our healthy participants as in previous work (Ziemann et al, 1993), our results indicated that SOL CSP might not be as reliable as RMT and latencies.…”

“…The reliability (intra-rater, inter-rater, and test-retest) of these measures in neurologically intact adults has been inconsistently examined in the past decade, partly due to the variation in methodology and laboratory set-up. These studies have demonstrated that some SOL (Gray et al, 2017, Lewis et al, 2014) and TA (Cacchio et al, 2009, Chung and Mak, 2015, Forster et al, 2014, Forster et al, 2012, Souron et al, 2016, Tallent et al, 2012, van Hedel et al, 2007) CMC measures can be reliably assessed in healthy adults, including resting and active motor thresholds, amplitude and latency of the motor evoked potential (MEP), and cortical silent period (CSP). Despite the valuable information that these studies have provided to the field, several methodological considerations make compilation of the reliability data difficult.…”

Integration of Convergent Sensorimotor Inputs Within Spinal Reflex Circuits in Healthy Adults

“…Short-interval facilitation (SIF) also often referred to as 'short latency facilitation of the H-reflex occurs when a subthreshold TMS pulse is delivered 1-5 ms after a PNS pulse, allowing the direct, fastest descending volley to arrive at the spinal LMN pool prior to the afferent signal, and enhance the H-reflex amplitude by modulating the excitability of the LMN pool (Nielsen and Petersen, 1995b;Gray et al, 2017). Long-interval facilitation (LIF), also referred to as long latency facilitation, occurs when a TMS pulse is delivered before PNS, allowing indirect, slower descending volleys to arrive prior to the afferent signal (Nielsen and Petersen, 1995b;Gray et al, 2017). Thus, SIF and LIF provide measures to non-invasively probe the specific sites and mechanisms of neuromotor circuit connections between cortical and spinal circuitry, which are previously poorly understood.…”