Brain stem auditory pathways involved in reflexive head orientation to sound.

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Abstract
Reflexive head movements in response to an unexpected sound were observed in normal cats and cats with lesions at the level of either the lateral lemniscus, brachium of the inferior colliculus, or auditory cortex. Measurements of the latency of the response were made from a piezoelectric accelerometer attached to the cat''s head. The initial position of the head, the direction of its initial movement and the accuracy of its final alignment with the sound source were measured by frame-by-frame analysis of videotapes recorded through a television camera mounted directly above the cat''s head. The direction of the initial reflexive movement of the head toward the source of an unexpected sound is mediated by nonlemniscal auditory pathways ascending to the vicinity of the inferior colliculus but not beyond. The accuracy of head orientation depends on the lemniscal pathway as high as the inferior colliculus and beyond that, on nonlemniscal tegmental pathways that bypass the superior colliculus.