| Research Abstract |
To elucidate spatial and cognitive function of the septal nuclei, neural activity was recorded from alert monkeys during performance of a place-dependent go-nogo (PGN) task in which response/reinforcement contingencies of given objects were conditional upon the location of a motorized, movable device (cab) containing a monkey in one of 4 places, and during two place-independent asymmetrical (AGN) and symmetrical (SGN) go-nogo tasks which required no conditional discrimination. Of 430 septal neurons recorded, the responses during the place phase in the 4 places were significantly different in 58 neurons. Responses of 8 of these neurons were also place-differential during the object phase as well as the place phase. Of 91 neurons responding differentially during the object Phase, 43 responded differentially only in the PGN task, 19 and 2 neurons were related to the reward-nonreward and go-nogo contingencies, respectively. The results suggest that septal nuclei are involved in integrating
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spatial information, conditional place-object relations, and reward/nonreward contingency.
To elucidate septal involvement in motivation/drive mechanisms, single neuron activity in the septal nuclei was recorded from water and food deprived monkeys during discrimination of objects associated with juice. Of 349 neurons recorded from two monkeys, 67 (45 excited ; 22 inhibited) responded in the ingestion phase. Of these 67 neurons, 31 were further tested with the clinical-liquid (juice or water) test in which liquid was provided until the animals became satiated. These 31 septal neurons were classified into two groups : type-I neurons (n=10) responded to juice ingestion with inhibition, and type-II neurons (n=21) with excitation. Spontaneous activity of the type-I, but not type-II, neurons were higher in deprived condition, and decreased as the animal became satiated by intake of liquid. Nine type-II neurons responded to the sight of a white object associated with juice as well as ingestion of juice in an operant discrimination task. The responses of these type II neurons to both the sight of white object and ingestion of juice also decreased by satiation. These changes in neural activities were well correlated to changes in motivational state. On the other hand, satiation by juice decreased not only the neural responses of type-II neurons to both sight of the white object and ingestion of juice, but also behavioral responses. Again, both the neural and behavioral responses resumed when the animal was tested with raisin. These types-I and II neurons were located mainly in the anterior part of the septal nuclei. The results suggest that the activity of type-I neuron might reflect thirst or hunger levels, and that responses of type-II neurons might be related to reward perception. Less
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