The nucleus of the basal optic root (nBOR) of the accessory optic system is known to be involved in the analysis of the visual consequences of self-motion. Previous studies have shown that the nBOR in pigeons projects bilaterally to the vestibulocerebellum, the inferior olive, the interstitial nucleus of Cajal, and the oculomotor complex and projects unilaterally to the ipsilateral pretectal nucleus lentiformis mesencephali and the contralateral nBOR. By using the anterograde tracer biotinylated dextran amine, we confirmed these projections and found (previously unreported) projections to the nucleus Darkshewitsch, the nucleus ruber, the mesencephalic reticular formation, and the area ventralis of Tsai as well as ipsilateral projections to the central gray, the pontine nuclei, the cerebellar nuclei, the vestibular nuclei, the processus cerebellovestibularis, and the dorsolateral thalamus. In addition to previous studies, which showed a projection to the dorsomedial subdivision of the contralateral oculomotor complex, we found terminal labelling in the ventral and dorsolateral subdivisions. Individual fibers were reconstructed from serial sections, and collaterals to various nuclei were demonstrated. For example, collaterals of fibers projecting to the vestibulocerebellum terminated in the vestibular or cerebellar nuclei; collaterals of fibers to the inferior olive terminated in the pontine nuclei; many individual neurons projected to the interstitial nucleus of Cajal, the nucleus Darkshewitsch, and the central gray and also projected to the nucleus ruber and the mesencephalic reticular formation; collaterals of fibers to the contralateral nucleus of the basal optic root terminated in the mesencephalic reticular formation and/or the area ventralis of Tsai; neurons projecting to the nucleus lentiformis mesencephali also terminated in the dorsolateral thalamus. The consequences of these data for understanding the visual control of eye movements, neck movements, posture, locomotion, and visual perception are discussed.

Abstract--Previous electrophysiological studies in pigeons have shown that the vestibulocerebellum can be divided into two parasagittal zones based on responses to optic flow stimuli. The medial zone responds best to optic flow resulting from self-translation, whereas the lateral zone responds best to optic flow resulting from self-rotation. This information arrives from the retina via a projection from the accessory optic system to the medial column of the inferior olive. In this study we investigated inferior olive projections to translational and rotational zones of the vestibulocerebellum using the retrograde tracer cholera toxin subunit B. Extracellular recordings of Purkinje cell activity (complex spikes) in response to large-field visual stimuli were used to identify the injection sites. We found a distinct segregation of inferior olive cells projecting to translational and rotational zones of the vestibulocerebellum. Translation zone injections resulted in retrogradely labeled cells in the ventrolateral area of the medial column, whereas rotation zone injections resulted in retrogradely labeled cells in the dorsomedial region of the medial column.Motion of any object through space, including self-motion of organisms, can be described with reference to translation and rotation in three-dimensional space. Our results show that, in pigeons, the brainstem visual systems responsible for detecting optic flow are segregated into channels responsible for the analysis of translational and rotational optic flow in the inferior olive, which is only two synapses from the retina. 1998 IBRO. Published by Elsevier Science Ltd.

Previous electrophysiological studies have shown that the pigeon vestibulocerebellum (ventral uvula, nodulus, and flocculus) can be divided into two parasagittal zones based on responses to optic flow stimuli. The medial zone (ventral uvula and nodulus) responds best to optic flow resulting from self-translation, whereas the lateral zone (flocculus) responds best to optic flow resulting from self-rotation. In this study we investigated the projections of the Purkinje cells in the translation and rotation zones of the vestibulocerebellum by using the anterograde tracer biotinylated dextran amine. Extracellular recording of Purkinje cell activity (complex spikes) in response to large-field visual stimuli were used to identify the injection sites. Injections into the translation zone resulted in extremely heavy terminal labeling in the cerebellovestibular process adjacent to the medial cerebellar nucleus. A moderate amount of terminal labeling was found in the medial cerebellar nucleus, the superior vestibular nucleus (laterally, dorsally, and medially), and the descending vestibular nucleus, particularly in the lateral half. Light terminal labeling was observed in the dorsolateral vestibular nucleus, the medial vestibular nucleus, the tangential nucleus, and the lateral vestibular nucleus pars ventralis. Injections into the rotation zone resulted in heavy terminal labeling in the superior vestibular nucleus (particularly dorsally and medially), the descending vestibular nucleus (particularly medially), and the medial vestibular nucleus. A moderate amount of terminal labeling was seen in the cerebellovestibular process adjacent to the lateral cerebellar nucleus, and the dorsolateral vestibular nucleus. A small amount of terminal labeling was found in the lateral cerebellar nucleus, the tangential nucleus, the prepositus hypoglossi, and the lateral vestibular nucleus pars ventralis.

In birds, optic flow is analyzed by two retinal-recipient nuclei: the nucleus of the basal optic root (nBOR) of the accessory optic system (AOS), and the pretectal nucleus, lentiformis mesencephali (LM). Previous anatomical studies have shown that both of these nuclei have descending projections to structures involved in oculomotor, head movement, and postural control. In this report, using biotinylated dextran amine (BDA) and cholera toxin subunit B (CTB) for anterograde and retrograde labelling, respectively, we investigated projections from the nBOR and LM to the dorsal thalamus. After injections of BDA into the nBOR and LM, terminals were consistently found in the nucleus dorsolateralis anterior pars lateralis and pars medialis, and the nucleus dorsalis intermedius ventralis anterior of the thalamus. Some terminals were also found in the nucleus dorsolateralis anterior, nucleus dorsomedialis anterior pars magnocellularis, nucleus dorsolateralis posterior, nucleus superficialis parvocellularis, and the ventrointermediate area. Injections of CTB into the dorsal thalamus resulted in retrogradely labelled cells in the pretectal region, including LM. Numerous cells were also seen in the nBOR pars lateralis and pars dorsalis, but fewer were seen in the nBOR proper. We suggest that the AOS is providing input to a thalamotelencephalic system that may be involved in several functions including: (1) multi-sensory analysis of self-motion, (2) perception of self-motion, (3) perception of the three-dimensional layout of the environment, (4) distinguishing object-motion from self-motion, and (5) spatial cognition.