Taste responses in the facial lobe of the carp, Cyprinus carpio L.

Single unitary discharges in the facial lobe of carp, Cyprinus carpio L., were studied electrophysiologically in response to chemical stimulation of the chemoreceptors of the facial skin. Of 258 neurons recorded, 95% were facilitated by taste stimuli and 5% were inhibited. According to responsiveness to the 4 basic tasting substances, the taste neurons were classified into 5 types: type I which was activated by one stimulus (43% of total neurons), type II by two (35%), type III by three (12%), type IV by 4 (5%), and type V which was inhibited by certain qualities (5%). Statical analysis revealed that responsiveness of taste neurons differed somewhat in receptive fields of the face. The taste neurons in the barbel and lip areas of the facial lobe showed variable responsiveness to chemical solutions, but those in other areas belonged generally to types I or II and did not respond to sucrose. Sodium chloride solution was the most effective among the 4 basic stimuli in this experiment. About 90% of the taste neurons also responded to mechanical stimulation of taste receptive fields. Tactile neurons in the facial lobe were localized in a topographical manner and the taste neurons were arranged in the tactile areas, but chemotopical organization was not recognized in the present study.