Afferentation of a caudal forebrain area activated during courtship behavior: A tracing study in the zebra finch (Taeniopygia guttata)

A caudal forebrain area of zebra finches that comprises a part of the caudal nidopallium and a part of the intermediate arcopallium is highly activated during courtship. This activation is thought to reflect the processing of information that is necessary for the choice of an appropriate mate. In addition to the information on the potential mate, control of courtship behavior includes motivational aspects. Being involved in the integration of external input and previously stored information, as well as in adding motivational factors, the caudal nidopallium and intermediate arcopallium should be integrative areas receiving input from many other regions of the brain. Our results indeed show that the caudal nidopallium receives input from a variety of telencephalic regions including the secondary visual and auditory areas. The intermediate arcopallium is recipient of input from intermediate and caudal nidopallium, mesopallium and densocellular hyperpallium. Regions closely associated with the song control nuclei also innervate both regions. There are also specific visual and auditory thalamic inputs, while specific motivating catecholaminergic mesencephalic afferents include the ventral tegmental area, the substantia nigra and the locus coeruleus. In addition, non-specific activation reaches these areas from the mesencephalic reticular formation. Bilateral innervation by ventral intermediate arcopallium indicates links with sensori-motor pathways, while the projection from the caudal nidopallium to intermediate arcopallium suggests monosynaptic and disynaptic input to downstream motor pathways. These findings support the idea of an involvement of the caudal nidopallium and the intermediate arcopallium in the control of courtship behavior.