Figure 5.

Neuronal connections between the trigeminal and vestibular sensory systems in birds. Putative magnetosensory locations, afferents, efferents and intratelencephalic connections. Known connections in pigeons are depicted as solid lines. Dashed lines indicate currently unknown, putative connections. The trigeminal sensory brain nuclei (PrV, SpV) receive direct input from V1-associated sensors located in or near the upper beak. PrV sends afferents to the telencephalic N. basalis via the quintofrontal tract (B). As shown by retrograde neuronal tracing, N. basalis receives input from superior vestibular nuclei (C). However, reciprocal projections originating from N. basalis have neither been shown for the vestibular nuclei (D) nor for the trigeminal nuclei (E). All major vestibular nuclei receive afferents from all semicircular and otolithic organs including the lagena (F). A recent study reported a direct connection between the lagena and SpV in chicken (G). No connections in either direction between the vestibular and trigeminal brainstem nuclei have been described at present (A,H). References: see main text.