Convergence of sleep-wakefulness subsystems onto single neurons in the region of cat's solitary tract nucleus.
Neurons in the region of cat's solitary tract nucleus were classified into three groups on the basis of their spontaneous discharge rate during slow wave sleep (SS) as compared with wakefulness (W): group I: SS greater than W; group II: SS less than W; and group III: SS divided by W. These three groups were further examined with regard to the modulation of discharge rate i) during motor activity in W, ii) at the transitional phase from SS to paradoxical sleep (PS), iii) during rapid eye movements (REMs) in PS, and iv) following electrical stimulation of the midbrain reticular formation (MRF). During motor activity in W, increase in unit discharge was frequently observed in group II, while group I and III were often associated with suppression. At the transitional phase from SS to PS many neurons showed a reduction in discharge rate. During REMs in PS, about a half of the neurons of each group responded with burst discharge. The responsiveness to electrical stimulation of the MFR was highest for the group I neurons and the lowest for the group III. The inhibitory responses tended to be smaller in magnitude during SS than during W. During PS, both excitatory and inhibitory responses were, in general, markedly diminished. The analysis of the results has suggested that groups I and II neurons may be involved in more multiple functions than group III neurons which have a tendency to maintain steady discharge rate.