Trial-to-trial fluctuations in H-reflexes and motor evoked potentials in human wrist flexor

The H-reflexes and the motor potentials (MEPs) evoked by electromagnetic brain stimulation in the human wrist flexor were recorded over many trials. The responses from each stimulus at two steady levels of muscle activation were sorted into three groups, based on their amplitudes. The electromyogram...

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Bibliographic Details
Published in:Neuroscience letters 1999-08, Vol.271 (1), p.25-28
Main Authors: Funase, Kozo, Miles, Timothy S, Gooden, Benjamin R
Format: Article
Language:English
Subjects:
Adult
Biological and medical sciences
Brain - physiology
Brain - radiation effects
Electromagnetic brain stimulation
Electromagnetic Fields
Electromyogram
Electromyography
Evoked Potentials, Motor - physiology
Fundamental and applied biological sciences. Psychology
H-reflex
H-Reflex - physiology
Humans
magnetoencephalography
Male
Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration
Motor evoked potentials
Muscle, Skeletal - innervation
Muscle, Skeletal - physiology
Vertebrates: nervous system and sense organs
Wrist Joint - innervation
Wrist Joint - physiology
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Summary:The H-reflexes and the motor potentials (MEPs) evoked by electromagnetic brain stimulation in the human wrist flexor were recorded over many trials. The responses from each stimulus at two steady levels of muscle activation were sorted into three groups, based on their amplitudes. The electromyogram (EMG) in each of these groups was rectified and averaged. The level of pre-response muscle activity was found to correlate with the amplitude of both the averaged H-reflexes and the averaged MEPs. This suggests that much of the amplitude fluctuations of both H-reflexes and MEPs can be attributed to moment-to-moment changes in the level of activity of the motoneurone pool. Overall, however, the amplitude of MEPs increased more rapidly than the amplitude of H-reflexes as the pre-stimulus EMG activity increased. This is probably because, while the amplitude of H-reflexes depends primarily on the level of motoneurone pool excitability, the amplitude of an MEP depends not only on this, but also on the excitability of the motor cortex, and the former is to some extent also dependent on the latter.
ISSN:0304-3940
1872-7972
DOI:10.1016/S0304-3940(99)00467-X