A physiological study of acoustic blinking reflex in the cat

Abstract

Blinking reflex was elicited by acoustic stimulus to investigate the reflex pathway in the encéphalo isolé cat. Reflex responses were recorded using electromyography (EMG) of the orbicularis oculi. The investigation was as follows: After stimulation by a loud click sound, the EMGs of the orbicularis oculi were elicited bilaterally. Latencies were 17-20 msec on the ipsilateral side, and 19-21 msec on the contralateral side. By electrical stimulation of the peripheral nerve in the cochlea and the acoustic nerve EMGs were also obtained. The latencies of the electrical stimulation responses correlated well with the latencies in the EMGs obtained through sound stimulation. The evoked potentials after auditory and electrical stimulation were obtained in several nuclei in the brainstem. The conduction time between two nuclei was calculated by measuring the latency of discharges in each nucleus. The alteration of the evoked discharge was observed through surgical transection of the brainstem. After each successive surgery the EMG showed differences in responses. Thus, the location of the neural connections of the pathways were differentiated in the brainstem. From this, we concluded that the reflex arc has the following pathway: The acoustic input to the ventral cochlear nucleus (VCN) is relayed to the acoustic route of the superior olivary complex and to the lateral lemniscus. Then, the impulse reaches the VIIth nucleus via the pontine reticular formation in the ipsilateral side. On the other hand, the input to the VCN crosses over the trapezoid body to the superior olivary complex. Then, the impulse uses the same pathway as described for the contralateral side. Finally, the pathway of the acoustic blinking reflex is located more caudally than that of the tactual blinking reflex. The comparison of the recordings of both reflexes is useful clinically, as a diagnostic method to study the function of the brainstem.