Standardization of H-reflex analyses

doi:10.1016/j.jneumeth.2006.11.020

Journal of Neuroscience Methods

Volume 162, Issues 1–2, 15 May 2007, Pages 1-7

https://doi.org/10.1016/j.jneumeth.2006.11.020 Get rights and content

Abstract

Variability in the H-reflex can make it difficult to identify significant changes using traditional pooled analysis techniques. This study was undertaken to introduce a normalisation approach to calculate both the relative size and the relative stimulus intensity required to elicit the H-reflex response so that comparisons can be made not only with results obtained during different experimental session but also between different subjects. This normalisation process fits the size of the measured M-responses and H-reflexes over the entire stimulus range with model curves to better facilitate the calculation of important parameters. This approach allows normalisation of not only the size of the response but also the relative stimulus intensity required to elicit the response. This eases the comparison of the reflex responses under various situations, and is capable of bringing out any genuine differences in the reflex in a reliable manner not previously possible. This study illustrates that comparison of the reflex between days is problematic, even in the same subject, as both the reflex size and the relative stimulus intensity required to obtain this reflex changed in all subjects. We suggest that H-reflex studies need to use normalisation not only for size of the reflex but also for the stimulus intensity, and also that all experiments for a single subject should be performed in the same session or during the same day using some level of background muscle activity in the muscle concerned as the variability of the muscle at rest was found to be larger.

Introduction

The H-reflex has been described as a monosynaptic reflex, and as an excellent tool in determining strength and distribution of spindle input to a motoneuronal pool (Hugon, 1973, Táboríková, 1973). However it cannot be described as a true direct measure of α-motoneuron excitability due to the pre-synaptic and postsynaptic effects on motoneuron excitability (for reviews see Capaday, 1997, Zehr, 2002). The H-reflex shape, and especially the latter part of the reflex, is known to have oligosynaptic contributions from the spindle afferents as well as the involvement of inhibitory Ib effects from Golgi tendon organs supporting further the non-monosynaptic nature of this reflex (Pierrot-Deseilligny et al., 1981, Burke et al., 1984).

The H-reflex is relatively easy to elicit, and has been used in many neurophysiological investigations in human to estimate a number of parameters that cannot be measured directly. These include: the effects of active or passive movements on the human soleus H-reflex (Brooke et al., 1995, Capaday and Stein, 1986), estimating synaptic efficacy of various sensory inputs to motoneuron pool (Crone et al., 1990, Meinck, 1980), estimating the threshold depolarisation of resting motoneurons (Türker and Miles, 1991), estimating the membrane potential trajectory (Türker, 1995), and estimating the strength of the Renshaw cell inhibition (Katz and Pierrot-Deseilligny, 1999). The reflex has also found a wide range of use in clinical neurophysiology (Downes et al., 1995, Misiaszek, 2003).

However, despite extensive reviews on this reflex (Capaday, 1997, Zehr, 2002) one particular aspect, the statistical analysis using standardized measurements remains ambiguous. It is possible that the variations in the H-reflex described in previous studies may have been due to a small number of stimuli being delivered (Zehr and Stein, 1999, Tucker and Türker, 2004), or a shift in the H-reflex recruitment curve due to a change in the position of the stimulating electrode/mixed nerve, and/or recording electrode/muscle relationship. In this paper a novel analysis method for the H-reflex is presented which uses normalisation for both the stimulus amplitude and the reflex size. We suggest that this new approach can elucidate genuine changes in the reflex circuitry and compensate for shifts in the H-reflex recruitment curve independent of the method used to determine the size of the reflex (area or peak-to-peak measurements; Tucker and Türker, 2005).

Section snippets

Methods

In order to illustrate the use of this new method three consenting adult volunteers took part in the study. The subjects were comfortably seated in a dental chair. The angle of the knee and foot joint, on both sides, was kept constant at ∼120^ο and 100^ο, respectively, by means of an immobile footplate. Because the soleus H-reflex can be influenced by posture (reviewed in Schiepatti, 1987) the head was supported on a headrest, and the forearms and hands were positioned at 0^ο pronation with the

Results

The trial-to-trial variability (within the 10 blocks of reflexes elicited at a given stimulus intensity) was noted in all subjects at all stimulus intensities. The variability was strongest at stimulus intensities that induced both H-reflexes and M-waves. A typical finding is illustrated in Fig. 1. Note that the stimuli were so arranged to include the lowest possible values to induce a minimum H-reflex and the highest possible values to generate a maximum M-wave. The number and distribution of

Discussion

There were a number of important findings in this study. Firstly, trial-to-trial variability was observed at all stimulus intensity levels, however the greatest variability existed at intensities that induced both the H-reflex and M-responses. Secondly, the importance of curve fitting and normalisation of the stimulus response curve to the M-response curve were illustrated. Thirdly, while H-reflex curves determined from experiments that were performed on the same day were similar, especially

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Standardization of H-reflex analyses

Abstract

Introduction

Section snippets

Methods

Results

Discussion

Clin. Neurophysiol.

J. Neurosci. Methods

J. Clin. Neurophysiol.

J. Electromyogr. Kinesiol.

Arch. Phys. Med. Rehabil.

Prog. Neurobiol.

Electroencephalogr. Clin. Neurophysiol.

Electroencephalogr. Clin. Neurophysiol.

J. Neurosci. Methods

J. Neurosci. Methods

Hum. Mov. Sci.

J. Electromyogr. Kinesiol.

J. Neurosci. Methods

Brain Res. Bull.

Changes in motoneurone firing rates during sustained maximal voluntary contractions

J. Physiol.

Amplitude modulation of the soleus H reflex in the human during active and passive stepping movements

J. Neurophysiol.

Monosynaptic and oligosynaptic contributions to human ankle jerk and H-reflex

J. Neurophysiol.