Abnormal motoneuronal excitability in hyperkinetic children.

Abstract

ABSTRACTTo investigate the generality of reported spinal monosynaptic reflex amplitude reductions in hyperkinetic children, H‐reflexes were recorded in unmedicated male hyperkinetic and age‐matched control children during relaxed wakefulness. Reflex amplitude variations were examined in response to either paired stimuli delivered at varying inter‐pair intervals (recovery function procedure) or trains of stimuli delivered at varying rates (homosynaptic depression procedure). As a group, hyperkinetic children demonstrated reflex amplitude reductions in the recovery function region of secondary facilitation (50–300 ms). However, these subjects could be divided into those showing either significantly exaggerated or reduced secondary facilitation relative to controls. Group differences present during paired‐stimuli procedures were maintained during repetitive stimulation. Furthermore, response reduction or enhancement in both paradigms extended beyond stimulus intervals encompassing the region of secondary facilitation. The results demonstrate that hyperkinetic children homogeneous for commonly utilized diagnostic criteria may exhibit disparate resting levels of spinal motoneuronal excitability which vary significantly from normal levels. Current thinking regarding bases for secondary facilitation and homosynaptic depression suggests the presence of both neurochemical and neurophysiological disregulation in hyperkinesis.