Organization of 'feeding circuits' in birds: pathways for the control of beak and head movements.

Two sensorimotor 'feeding' circuits and their descending projections are described in the mallard and compared to those in the pigeon. The tactile/trigeminal circuit consists of a pattern of reciprocal connections of the nucleus basalis with the overlying parts of the frontal neostriatum (Nf) and hyperstriatum ventrale (HV). The dorsal zone of Nf projects to the sensorimotor part of archistriatum, to the paleostriatum augmentatum (PA) and to the lateral lobus parolfactorius. A comparable pattern of visual connections has been found: the ectostriatum has reciprocal connections with the intermediate neostriatum (Ni) and HV. Here, too, Ni has projections to archistriatum and probably to PA. Archistriatum is the source of a large descending pathway with, among others, substantial projections to the parvocellular reticular formation of the brain stem. This provides a pathway for telencephalic control of premotor systems of jaw, tongue and neck muscles. The paleostriatal complex is the source of the ansa lenticularis with projections to the nucleus spiriformis lateralis and the nucleus tegmenti pedunculopontinus, both projecting to the deep tectum. This pathway may be important for the control of body position. In the mallard, it includes a substantial trigeminal component that has not been found in the pigeon.