Technique for studying synaptic connections of single motoneurones in man

Abstract

DURING normal voluntary muscle contractions, the pattern of discharge of a single motoneurone is determined by the summed effects of an enormous variety of different types of synaptic input. In principle, the effect of any one of these inputs could be determined by constructing a histogram of the time of occurrence of motoneurone spikes after repeated presentation of a suitably controlled stimulus^1,2. This procedure extracts from the naturally occurring spike train only those changes in firing time locked to the stimulus. The synaptic effect of a given input is thus revealed in terms of the specific contribution it makes to the total firing pattern of the cell. Such studies are most conveniently carried out in man where the cooperation of the subject is invaluable. This report describes an example of this approach in the study of the synaptic effects of a simple cutaneous input. In more general terms, the experimental situation described enables, for the first time, the synaptic connections of single motoneurones to be examined in man, studies previously only attempted in anaesthetised or decerebrate animals.