A propriospinal-like contribution to electromyographic responses evoked in wrist extensor muscles by transcranial stimulation of the motor cortex in man

摘要: We tested the hypothesis that some of electromyographic (EMG) responses elicited in preactivated forearm muscles by transcranial stimulation human motor cortex are produced activity a disynaptic corticospinal linkage involving propriospinal-like interneurones with cell bodies spinal C3-4 segments. The experimental design incorporated previous observation afferents superficial radial nerve inhibits neurones projecting to extensor carpi radialis (ECR) muscle. Surface EMG were recorded from active ECR muscle after electrical or magnetic over cortex. In random trials, single conditioning stimuli at twice perceptual threshold given wrist different times before cortical shock. When was stimulated electrically, stimulus suppressed when interval between shocks 11 ms more. This about 3.5 longer than minimum time calculated for possible direct cutaneous effect on motoneurones. course suppression began earlier and more complex during It is argued this difference due repetitive I waves generated Whether used, first 1-3 response relatively unaffected any interstimulus interval, whereas clear seen later portion response. contrast, if median elbow, then all portions inhibited including ms. thought be reciprocal inhibition Thus sparing initial part cortically evoked suggests latter type occurs premotoneuronal level. timing compatible explanation excitation motoneurones through both monosynaptic (including propriospinal premotoneuronal) pathways, being exerted