Effects of homosynaptic depression on spectral properties of H-reflex recordings

Abstract

The purpose of this study was to determine the effects of homosynaptic depression (HD) on spectral properties of the soleus (SOL) H-reflex. Paired stimulations, separated by 100 ms, were used to elicit an unconditioned and conditioned H-reflex in the SOL muscle of 20 participants during quiet standing. Wavelet and principal component analyses were used to analyze features of the time-varying spectral properties of the unconditioned and conditioned H-reflex. The effects of HD on spectral properties of the H-reflex signal were quantified by comparing extracted principal component scores. The analysis extracted two principal components: one associated with the intensity of the spectra and one associated with its frequency. The scores for both principal components were smaller for the conditioned H-reflex. HD decreases the spectral intensity and changes the spectral frequency of H-reflexes. These results suggest that HD changes the recruitment pattern of the motor units evoked during H-reflex stimulations, in that it not only decreases the intensity, but also changes the types of motor units that contribute to the H-reflex signal.

Paired associative transspinal and transcortical stimulation produces plasticity in human cortical and spinal neuronal circuits

“…Repetitive transcortical-transspinal PAS may have altered the recruitment pattern of SOL motor units, a phenomenon associated with SOL H-reflex postactivation depression (Kipp et al 2012). However, we should also consider the possibility that postsynaptic inhibition, exerted from synergistic Ib afferents and antagonistic Ia afferents, may adapt differently to paired and frequency-dependent afferent discharges.…”

Methods for automated delineation and assessment of EMG responses evoked by peripheral nerve stimulation in diagnostic and closed-loop therapeutic applications

“…The present study describes a novel waveletbased algorithm for automatically determining the bounds of the H-reflex and M-wave in the human soleus muscle, and quantifies the agreement between recruitment-curve parameters derived from bounds output by the algorithm and bounds chosen manually by a human expert. Wavelets are well-suited to H-reflex and M-wave modeling and have been applied for separation of muscle sources, evaluation of spectral properties, and prediction of motor output from EMG [23][24][25]. The present study reports a novel application of the Morlet wavelet for detecting the temporal limits of these evoked potentials.…”