The main sensory trigeminal nucleus in the pigeon: A single‐unit analysis

A single‐unit analysis of the main sensory trigeminal nucleus of the pigeon was carried out. A total of 130 units from 20 birds were isolated and their modality, adaptive properties and receptive field characteristics were defined. Seventy‐two percent of the cells were activated by mechanical stimulation ranging from very light touch to pressure. Receptive field areas were generally less than five mm2 in extent. Six units had receptive fields in the region of the orbit, but the receptive fields of most units were confined to the ipsilateral dorsal or ventral beak. Both inner and outer beak surfaces were represented, but no units responsive to tongue stimulation were encountered. Somatotopic organization was evident only in the dorso‐ventral plane where there was a clear sequence of representation from mandibular to maxillary to opthalmic areas. Of the units responsive to mechanical stimulation, 60% were slowly‐adapting, 40% were fast‐adapting. A number of cells (28%) were driven by opening or closing the mouth. Most of these signalled the displacement by a change in their steady discharge rate; a few cells responded to beak displacement with a transient burst. These results clarify the nature of the feeding deficits produced by lesions of the main sensory trigeminal nucleus and suggest an involvement of the nucleus in the sensory control of mandibulation during feeding in the pigeon.