MOTIVATION-RELATED NEURONAL-ACTIVITY IN THE OBJECT DISCRIMINATION TASK IN MONKEY SEPTAL NUCLEI

Septal nuclei are suggested to work as an interface between the hippoc ampal formation, involved in higher cognitive functions, and the hypot halamus, involved in motivational behaviors such as feeding, drinking, and intracranial self-stimulation. In the present study, to elucidate a role of the septal nuclei in motivational behaviors, single neuron activity was recorded from water-and food-deprived monkeys during disc rimination of objects associated with juice, and during ingestion of j uice. Of 349 neurons recorded from two monkeys, 67 responded in the in gestion phase of the object discrimination task. Of these 67 neurons, 31 were further tested with the noncontingent liquid (juice or water) test in which liquid was provided until the animals became satiated. T hese 31 septal neurons were classified into two groups: type I neurons (n = 10) responded to juice ingestion with inhibition, and type II ne urons (n = 21) responded with excitation. The spontaneous firing rates of the type I neurons were higher in the deprived condition and decre ased as the animal became satiated by intake of liquid. Nine type II n eurons responded to the sight of a white object associated with juice as well as ingestion of juice. The response magnitudes of the type II neurons to both the sight of the white object and ingestion of juice a lso decreased by satiation. However, spontaneous firing rates of the t ype II neurons did not change. These activity changes of both type I a nd II neurons were well correlated with changes in motivational state of the monkey estimated by the behavioral test. The results suggest th at the activity of type I neurons reflects thirst or hunger drive leve ls, and that responses of type II neurons are related to reward percep tion. These type I and II neurons were located mainly in the anterior part of the septal nuclei. Results of the present study suggest, along with previous lesion and anatomical studies, that the septal nuclei e xert a powerful influence on the motivational/drive systems through th e projection to the hypothalamus. (C) 1997 Wiley-Liss, Inc.