title: The relationship between the soleus H-reflex amplitude and vibratory inhibition in controls and spastic subjects. II. Computer model.
abstract: A computer model is presented that describes soleus H-reflex recruitment as a function of electric stimulus intensity. The model consists of two coupled non-linear transfer functions. The first transfer function describes the activation of muscle spindle (Ia) afferent terminals as a function of the electric stimulus intensity; whereas the second describes the activation of a number of motoneurons as a function of the number of active Ia afferent terminals. The effect of change in these transfer functions on the H-reflex recruitment curve is simulated. In spastic patients, a higher average maximal H-response amplitude is observed in combination with a decreased H-reflex threshold. Vibration of the Achilles tendon reduces the H-reflex amplitude, presumably by reducing the excitatory afferent input. Vibratory inhibition is diminished in spasticity. In the model, the afferent-motoneuron transfer function was modified to represent the possible alterations occurring in spasticity. The simulations show that vibratory suppression of the H-reflex is determined only in part by the inhibition level of the afferent input. With a constant level of presynaptic inhibition, the suppression of reflexes of different sizes may vary. A lowering of the motoneuron activation thresholds in spastic patients will directly contribute to a decrease of vibratory inhibition in spasticity.
authors: Department of Neurology, Clinical Neurophysiology unit (D2), Academic Medical Center, Amsterdam, The Netherlands.
authors: A A
authors: AA
authors: Hilgevoord
authors: L J
authors: LJ
authors: Bour
authors: J H
authors: JH
authors: Koelman
authors: B W
authors: BW
authors: de Visser