The "goatee" of Goatfish : innervation of taste buds in the barbels and their representation in the brain

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Goatfishes use a pair of large chin barbels to probe the sea bottom to detect buried prey. The barbels are studded with taste buds but little else is known about the neural organization of this system. We find that the taste buds of the barbel are innervated in a strict orthogonal fashion. The barbel is innervated by a main nerve trunk running in the core of the barbel. A longitudinal nerve bundle originates from the main trunk and after running a short distance distally, divides into two circumferential nerve bundles (CNB) extending respectively, medially and laterally around the barbel. Approximately 15 CNBs innervate each 1 mm length of barbel. At each transverse level, the CNB innervates two clusters of taste buds each containing 14 end organs. The primary taste center in the brain is similarly extraordinary. The sensory inputs from the barbel terminate in a derived dorsal facial lobe which has a highly convoluted surface forming a multitude of tubercles.Electrophysiological mapping experiments show the entire barbel is somatotopically represented as a recurved elongate tubular fashion within the dorsal facial lobe.The neural representation of the chin barbels of goatfish is highly unusual both in terms of the orthogonal regularity of the peripheral innervation and in their representation in a tortuous, recurved somatotopy. The system appears specialized to permit the fish to accurately discern the depth of a prey object buried in the sand.