Do muscle afferents contribute to the cervical response evoked by electrical stimulation of the median nerve in man?
The possible contribution of low threshold muscle afferents to the postsynaptic component (N13) of the cervical response evoked by electrical stimulation of the median nerve (MN) was investigated in normal subjects. Electroneurographic (ENG) and electromyographic (EMG) correlates of the reflex motoneuronal discharge (RMND) were recorded simultaneously. A. No reflex activity could be elicited by stimulation of the MN at the wrist, at least in the resting subjects, while well developed ENG (P2 efferent volley) and EMG (H reflex) monosynaptic responses occurred following stimulation of the MN at the elbow at suitable strengths. In neither case could a surface correlate of interneuronal activity evoked by muscle afferents be demonstrated. B. Recruitment curves showed that at stimulus intensities above maximal for the H reflex both P2 and H responses started to decrease until they completely disappeared, while N13 showed further enhancement. C. Subthreshold conditioning stimulation of the M
