Organization of the afferent projections to the Wulst in the pigeon

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Abstract
The afferent connections to the Wulst, a well‐defined bulge in the fore‐brain roof, were studied in the pigeon. Cells of origin were identified by horseradish peroxidase retrograde tracing, after placing multiple injections in the Wulst. The results demonstrate a bilateral intratelencephalic pathway arising from the archistriatum intermedium (Ai) in the basal forebrain. Labeled cells in n. superficialparvocellularis (SPC) and n. dorsolateralis posterior (DLP) on both sides of the brain, provide anatomical evidence for a bilateral forebrain projection of the somatosensory thalamus. A sparse ipsilateral input of unknown function from the medial thalamus originates in n. dor‐somedialisanterior(DMA)and n. dorsolateralis medialis (DLM).Weprovide confirminge vidence of the bilateral thalamofugal visual pathway ascending from nuclei of the dorsolateral thalamus (DLAmc and DLL). Projections from several brain stem structures are described, including: griseum cen‐trale (GCt), medial and lateral reticular formation (FRM and FRL), area ventralis of Tsai (AVT), n. annularis (Anl), locus coeruleus (LoC), and the avian homologue of the raphe nucleus, n. linearis caudalis (LC). The account provides a direct anatomical demonstration of a Wulst input from the basal forebrain, the somatosensory thalamus, and the brain‐stem. The projection cells in the brainstem reside in structures known to contribute to ascending catecholaminergic and serotoninergic pathways.