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SUMMARY A crossed short latency component (Ri) of the human blink reflex could be elicited in orbicularis oculi muscles to stimulation of the contralateral supraorbital nerve, when infraliminal conditioning stimuli were applied to various cutaneous afferents of the body (facial, upper and lower limbs). The crossed Rl responses appeared when the time interval between the conditioning and the test stimuli was of 30 to 40 ms, 50 to 65 ms and 95 to 110 ms for facial, upper and lower limbs afferents respectively. For the same time intervals, these conditioning volleys also exerted a facilitatory effect on the ipsilateral Rl responses. Furthermore, crossed Rl responses were also obtained during supraspinal facilitation induced by a voluntary contraction of the eyelids. These data show that crossed oligosynaptic trigemino-facial reflex connections exist in normal subjects, which become functional when adequate conditioning stimuli are available.Electrical stimulation of supraorbital nerve results in a well known double trigemino-facial reflex discharge of EMG activity (Rl and R2) in the ipsilateral orbicularis oculi muscle and a single discharge (R2) in the contralateral muscle.'4 The early ipsilateral component (R1) is transmitted through an oligosynaptic arc in the pons.56 The late bilateral component (R2) follows a long polysynaptic pathway travelling through the spinal nucleus of the trigeminal nerve.6' Although direct anatomical connections between the trigeminal sensory nucleus and the contralateral facial nucleus have been described,8 most authors agree on the strictly ipsilateral distribution of RI. However the occasional crossed character of this early response has been reported in both healthy subjects9 and patients with post-facial palsy mass contractions.'0"1 The aim of the present study was to investigate whether these contralateral early responses (R1) are produced by abnormal synaptic connections or by existing

Seven patients with postfacial palsy contracture and mass contractions were investigated electrophysiologically. In 3 patients the early blink reflex showed an unusually high amplitude, which can be attributed to enhanced excitability of facial motor neurons. In 5 patients the early blink reflex had acquired a crossed character. It is assumed that changes in organization of the facial nucleus contribute to the altered function of reinnervated facial muscles.

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