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Fractal correlation in human H-reflex

D Nozaki¹, K Nakazawa, Y Yamamoto

¹Laboratory for Exercise Physiology and Biomechanics, Graduate School of Education, University of Tokyo, Japan.

Experimental Brain Research

|January 1, 1995

Summary

The human H-reflex exhibits fractal properties and strong time correlations, suggesting spinal cord synaptic connections generate this variability. This contrasts with the M-wave, indicating the H-reflex

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Area of Science:

Neuroscience
Biophysics
Physiology

Background:

The H-reflex amplitude shows significant variability, even with constant stimulation.
Previous research has overlooked the time-dependent nature of this variability.
Fractal properties, characterized by self-similarity and long-range temporal correlations, have been identified in complex biological signals.

Purpose of the Study:

To investigate if H-reflex fluctuations exhibit fractal characteristics with strong time correlations.
To determine the origin of fractal correlations in the H-reflex signal.

Main Methods:

Soleus H-reflexes were recorded in five healthy subjects at two stimulation intensities (1.2 and 0.9 motor threshold).
Successive H-wave and M-wave amplitudes (1050 each) were recorded every second.
Coarse-graining spectral analysis was used to calculate fractal components (%Fractal) and spectral exponents (beta).

Main Results:

H-wave and M-wave sequences showed high fractal components (>90%).
H-wave sequences exhibited non-flat power spectra (beta ≈ 0.75-0.80), indicating strong time correlation.
M-wave sequences displayed flatter spectra (beta ≈ 0.26), similar to uncorrelated white noise.

Conclusions:

The fractal correlation in H-waves is not due to nerve conduction or neuromuscular junction transmission, as evidenced by weaker M-wave correlation.
Antidromic impulses contribute minimally to H-reflex fractal correlation.
Fractal correlation in human H-reflex likely originates from synaptic connections to alpha-motoneurons in the spinal cord.

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