[Fractionated determination of central motor conduction times using stimulation of the cortex, spinal tract and spinal nerve roots: possibilities and limits].

Two different approaches of determining central motor conduction times were investigated. Both methods were based on calculations of latency differences of muscle compound action potentials. First, using multilocal stimulation of the descending motor system at different levels (motor cortex, motor tracts at spinal level, motor roots) and recording from one reference muscle (Figs. 1 and 2). Second, using unilocal stimulation over the motor cortex and recording from a number of paravertebral muscles at levels from C7 to L5 (Figs. 3 and 4). With multilocal stimulation of the motor pathways, muscle response potentials are observed which differ in amplitude, duration and configuration depending on the site of stimulation (Figs. 1 and 2). This finding points to the incongruency of excited fibres within the descending motor pathways. The causes underlying this phenomenon and the resulting limitations for determining central motor conduction times are discussed. The new approach using recordings of cortically evoked responses on different levels in paravertebral muscles does not suffer from the methodical limitations of the multilocal stimulation and may be of higher clinical validity for the localization of circumscript spinal processes.