[Regulation of the theta activity of septal neurons by cortical and brain stem structures].

Neuronal rhythmic burst activity was recorded extracellularly in the intact septum (34 cells) and in septum deprived of hippocampal connections (100 cells) during electrical stimulation of various neocortical areas, midbrain and pontine reticular formation, and medial forebrain bundle (MFB) in the preoptic area. All structures tested influenced burst production in septal cells. Cortical influences might phasically trigger or regularize theta-activity, but more often they suppressed and desynchronized it. The reticular stimulation tonically increased frequency, regularity, and density of the theta-bursts. MFB influences were similar, but less effective. Increasing the intensity of the stimulating current resulted in a logarithmic increase of theta-burst frequency up to the upper limit of the EEG theta-frequencies (9-10 Hz). Short electrical or sensory stimulation reset the burst activity so that the series of bursts followed each other for several seconds in a stable pattern, which was reproduced by each next application of the same stimulus. Regulation of the theta-rhythm by direct influences upon various types of septal units without hippocampal involvement is discussed.