Studies on the somatotopy of the trigeminal system in the mallard, Anas platyrhynchos L. IV. Tactile representation in the nucleus basalis.

This electrophysiological study complements neuroanatomical work from our department on the somatotopy of the trigeminal system of the mallard. Peripheral areas of mechanoreceptors in bills and tongue were mapped in the telencephalic nucleus basalis, a second-order relay nucleus in the ascending trigeminal pathway. The multi-unit responses recorded under Equithesin anaesthesia did not show spontaneous activity and all animals adapted rapidly after mechanical stimulation. They showed well-circumscribed receptive fields whose peripheral position did not change when the electrode was lowered in the vertical stereotaxic plane, but changes immediately when its position was changed in the horizontal XZ-plane. The somatotopic picture presented here corresponds in many details to that obtained with combined neuroanatomical techniques (Dubbeldam et al., '81). In the discussion the structural point-to-point relationship between the peripheral mechanoreceptive areas and the nucleus basalis is tentatively changed to a division into areas related to the functional units involved in the subsequent sensory events during feeding. The somatotopy provides a basis for future chronic experiments to investigate this postulated role of the various areas in the nucleus basalis.