COMPARISON OF CORTICOMOTONEURONAL EPSPS AND MACRO-MUPS IN AMYOTROPHIC-LATERAL-SCLEROSIS

We correlated the size of the corticomotoneuronal excitatory postsynap tic potential (CM-EPSP) arising in a single spinal motor neuron with t he function of the target motor unit as measured by conventional and m acro EMG in early amyotrophic lateral sclerosis (ALS). Macro motor uni t potentials (macro-MUPs) were recorded from a surface electrode after spike-triggered averaging in the extensor digitorum communis muscle, The size of the CM-EPSP projecting to the same motor unit was measured from changes in the firing probability of single motor units induced by transcranial magnetic stimulation using peristimulus time histogram s. In controls, the amplitudes of CM-EPSPs and macro-MUPs correlated i nversely, probably reflecting a lower input resistance of larger spina l motoneurons. In ALS the amplitude of macro-MUPs did not correlate wi th that of CM-EPSPs and one third of normal ALS motor units had a redu ced or temporally dispersed CM-EPSP. The findings indicate primary dys function of the corticomotoneuronal projection system in ALS that is i ndependent of functional changes of spinal motoneurons. (C) 1998 John Wiley & Sons, Inc.