A Pallial Visual Area in the Telencephalon of the Bony Fish <i>Polypterus</i>

Abstract

The dorsal (P2) and lateral (P3) pallial zones of bichirs receive a substantial projection from nucleus medianus of the posterior tuberculum. Although nucleus medianus does not receive a direct retinal input, its close proximity to ascending tectal efferents suggests that it might receive a tectal input and form a segment of a retinotectal-tubercular pathway to the pallium. In order to test this possibility, evoked responses to light flashes were electrophysiologically recorded and tectal efferents were experimentally determined in bichirs. These experiments suggest that a single visual field exists across the dorsal and lateral pallial zones and that this field is mediated by nucleus medianus, which does receive a direct tectal projection. This visual pathway appears to be uniquely derived and not homologous to any other known pathway in tetrapods. Furthermore, these results support the contention that the P2 and P3 pallial zones in bichirs are subdivisions of a single pallial zone.