Projections of the oval nucleus of the hyperstriatum ventrale in the budgerigar: Relationships with the auditory system

The afferent and efferent projections of a vocal control nucleus, the oval nucleus of the hyperstriatum ventrale (HVo), were mapped out in a parrot, t he budgerigar (Melopsittacus undulatus) to determine the relationships of t his nucleus to the auditory system. In budgerigars, HVo is connected to bot h the anterior forebrain pathway as well as to nuclei forming the descendin g projection system to the brainstem (Durand et al. [1997] J. Comp. Neurol. 377:179-206). Previous studies (Brauth et al. [1997] Proc. N. Y. Acad. Sci . 807:368-385; Durand and Brauth [1998] Neurosci Abstr 24:78.9) indicate th at HVo lesions disrupt vocal performance and that HVo neurons show long lat ency electrophysiologic auditory responses. HVo has also been shown to rece ive input from neurons in the immediately adjacent HV (Durand et al. [1997] J. Comp. Neurol. 377:179-206). Thus, the focus of the present study was to elucidate relationships between HVo, its immediately adjacent surround and telencephalic auditory nuclei. The results show that, although the lateral and medial portions of HVo are interconnected with one another, inputs to these areas and their surrounds are distinctively different. The most subst antial auditory system inputs are derived from the frontal lateral neostria tum (NFl) and supracentral nucleus of the lateral neostriatum (NLs); these project primarily to the lateral HVo and lateral HVo surround. The medial H Vo and surround receive only sparse or modest input from auditory nuclei, i ncluding the caudomedial neostriatum (NCM), neostriatum intermedium pars la teralis (NIL), Fields L1 and L3, and the neostriatum intermedium pars ventr olateralis (NIVL). Other sources of input to the HVo surround include the h yperstriatum accessorium (HA), the supralaminar area of the frontal neostri atum (NAs), the ventral anterior archistriatum (AAv), the medial archistria tum (Am) and the medial HV. Neurons in the HV immediately medial to HVo pro ject to a shell region around the entire nucleus. Both the ventral paleostr iatum (VP) and ventral part of the central nucleus of the lateral neostriat um (NLc) project to HVo but not to the surround; Previously described proje ctions (Durand et al., 1997) from HVo to the NAom, NLc, and the magnicellul ar nucleus of the lobus parolfactorius (LPOm) were confirmed. (C) 2001 Wile y-Liss, Inc.