ANATOMICAL BASIS FOR AUDIO-VOCAL INTEGRATION IN ECHOLOCATING HORSESHOE BATS

Neurophysiological recordings suggest that audio-vocal neurons located in the paralemniscal tegmentum of the midbrain in horseshoe bats prov ide an interface between the pathways for auditory sensory processing and those for the motor control of vocalization. To verify these physi ological results anatomically, the projection pattern of the audio-voc ally active area in the paralemniscal tegmentum was investigated by us ing extracellular tracer injections of wheat germ agglutinin conjugate d to horseradish peroxidase. Several nuclei of the lemniscal auditory pathway (dorsal nucleus of the lateral lemniscus, central nucleus of t he inferior colliculus, lateral superior olive) as well as the nucleus of the central acoustic tract appear to project to the paralemniscal tegmentum. Other possible sources of afferent projections are a small but distinctly labeled structure within the lateral hypothalamic area, the substantia nigra pars compacta, the deep mesencephalic nucleus, t he rostral portion of the inferior colliculus, the deep and intermedia te layers of the superior colliculus, and several small areas in the r hombencephalic reticular formation. No direct efferent projection from the audio-vocally active area of the paralemniscal tegmentum to prima rily auditory structures was found. Instead, the main targets were str uctures that are involved in the control of different motor patterns. These targets include the deep and intermediate layers of the superior colliculus and the dorsomedial portion of the facial nucleus, both of which most probably control pinna movements in cats, and the reticula r formation medial and caudal to the facial nucleus and rostral to the nucleus ambiguus, which represents an area involved in the control of vocalization. Hence, the anatomical projection pattern suggests that the paralemniscal tegmentum in horseshoe bats serves as a link between the processing of auditory information and the control of vocalizatio n and related motor patterns. (C) 1996 Wiley-Liss, Inc.