ERG alterations induced by sound.

The existence of efferent neurons from the CNS to the retina mediating centrifugal effects is an old and much debated hypothesis. In order to test whether the human ERG can be influenced by another sensory input, we have recorded the retina response to light when a sound was presented simultaneously. It was found that the b-wave of the ERG increased when a flash was paired with a sound. The sound-induced increment of the b-wave showed the following characteristics: a) Short time course, b) No relation to the frequency and intensity of the sound, c) Habituation specific to the frequency of the sound, d) Adaptation when the sound lasted more than 2 sec, e) Dependence on localization cues of the sound and f) Enhancement by low doses and suppression by high doses of diazepam. Further experiments on rabbits showed that it is not suppressed by ether anesthesia, by local application of atropine or by cutting the external ocular muscles. The results suggest that this effect is brought about by a reticulo-retinal pathway, the function of which is most probably to control the input of the visual route.