Brain stem generation of the hippocampal EEG.

In summary, based on unit recording studies in behaving animals it appears that the brain stem cells best suited for a role in theta generation are the pontine RF neurons in the rat (Vertes, 1980, 1981) rabbit (Klemm, 1970) and dog (Arnolds, 1977) that fire selectively during the identical states in which theta is present in the hippocampus and whose discharge characteristics closely parallel properties attributed to hippocampal theta (Vertes, 1981). The omission of any description of RF cells in the behaving cat with theta-like properties (McCarley and Hobson, 1971; Hobson et al., 1974; Siegel et al., 1977, 1979) could stem from any of the following factors: (1) species differences; (2) differences in RF recording sites; (3) failure of the cat studies to specifically evaluate RF cell discharge in relation to hippocampal theta. The only other brain stem nucleus directly implicated in theta generation in unit recording studies was the raphe magnus (Sheu et al., 1974). The firing of cells within other monoaminergic nuclei including the locus coeruleus was unrelated or only loosely related to states of hippocampal synchronization or desynchronization (Sheu et al., 1974; Chu and Bloom, 1973, 1974; Hobson et al., 1975; Foote and Bloom, 1979; Aston-Jones and Bloom, 1981; Heym et al. 1981).