Interrelationship among multiunit activity of the midbrain reticular formation and lateral geniculate nucleus, thalamocortical arousal, and behavior in rats.

Analyses of multiunit activity of midbrain reticular formation (RF) and lateral geniculate nucleus (LG) revealed marked phasic covariation that conformed to characteristics of behavior. Movement patterns appeared to set the range within which RF activity and thalamocortical arousal (as reflected in LG activity) varied. In tests of spontaneous behavior, sensory stimulation, bar pressing for food, and conditioned emotional response. RF activity and thalamocortical arousal conformed to immediate properties of behavior apart from conditions giving rise to the behavior. Other analyses revealed close relationships between RF activity and visual evoked response, but only a general relationship to hippocampal slow-wave rhythms. Our findings emphasize the necessity for refining psychological conceptualizations of arousal processes.