Examination of central and peripheral motor pathways by standardized magnetic stimulation

A standardized magnetic stimulation procedure for evaluation of central and peripheral motor pathways is described together with the results of motor evoked potential (MEP) recordings from 6 muscles in 50 healthy volunteers aged 18 to 60 years. Facilitation of the neuronal pathways was standardized using the integrated electric activity of the EMG as a gauge. The target muscles were: the brachial biceps (BB), the radial carpal flexor (FCR), the first dorsal interosseus of the hand (FDI), the medial vastus of the quadriceps muscle (VM), the anterior tibial (TA) and the abductor hallucis muscles (AH). The parameters used were the conduction times and the amplitudes of the CMAPs evoked by brain and root stimulation. CMAPs could be recorded from all muscles in all but three subjects in whom cortical stimulation was unsuccessful in one TA and two AHs, while root stimulation was negative in two TAs and one AH. Height and conduction times were significantly correlated, while age and conduction times were not. By linear regression 30-60% of the variation in the conduction times could be explained by the variation in height. The residual variation of the conduction times was less than in most other non-standardized studies and comparable to peripheral electrical motor conduction studies.