Task-related changes of transmission in the pathway of heteronymous spinal recurrent inhibition from soleus to quadriceps motor neurones in man

• Published in: Brain (London, England : 1878) Vol. 123; no. 11; pp. 2264 - 2272
• Main Authors: Iles, J. F., Ali, Alima, Pardoe, Joanne
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.11.2000; Oxford Publishing Limited (England)
• Subjects: Action Potentials - physiology; adjC/T% = ratio of conditioned to test reflex amplitude; adjusted if the conditioning soleus motor discharge differed from 35%Mmax; Adult; Biological and medical sciences; C/T% = conditioned reflex amplitude divided by test reflex amplitude; Conditioning (Psychology) - physiology; Electric Stimulation; Exercise - physiology; Female; Fundamental and applied biological sciences. Psychology; GLM = General Linear Model; H-Reflex - physiology; human; Humans; Male; Middle Aged; Mmax = percentage of the maximum motor discharge; Motor Activity - physiology; motor control; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Motor Neurons - cytology; Motor Neurons - physiology; Muscle Contraction - physiology; Muscle Spindles - cytology; Muscle Spindles - physiology; Muscle, Skeletal - innervation; Muscle, Skeletal - physiology; MVC = percentage of maximum voluntary contraction; Neural Inhibition - physiology; Neural Pathways - cytology; Neural Pathways - physiology; Psychomotor Performance - physiology; recurrent inhibition; Regression Analysis; spinal cord; Spinal Cord - cytology; Spinal Cord - physiology; Synaptic Transmission - physiology; Vertebrates: nervous system and sense organs; Human; Spinal cord; Quadriceps muscle; Physiology; Inhibition; Recurrent; Soleus muscle; Motor control
• ISSN: 0006-8950; 1460-2156
• DOI: 10.1093/brain/123.11.2264

An H reflex conditioning technique was used to monitor the transmission of heteronymous recurrent inhibition from soleus to quadriceps motor neurones of the human lower limb. Inhibition declined during quadriceps muscle contraction under all conditions examined, falling to zero at around one-third of the maximum voluntary contraction. Inhibition declined during soleus muscle contraction in sitting, standing and bicycling tasks. The level of inhibition assessed at a given (weaker than 30%) level of quadriceps contraction was reduced during postural tasks involving quadriceps and soleus co-contraction (standing and late-stance phase of walking) when compared with sitting and performing matched voluntary muscle contractions. The level of inhibition during the mid-power stroke of a bicycling task, which also involved co-contraction of quadriceps and soleus, was greater than during matched voluntary muscle contractions while sitting. It is concluded that the pathway of heteronymous recurrent inhibition from soleus to quadriceps motor neurones is under at least two types of control: one related to the task, which sets the operating range, and a second which couples inhibition to the level of muscle contraction. Multiple control pathways are consistent with the diverse effects on recurrent inhibition reported in subjects with upper motor neurone lesions.