The frequency of rat's hippocampal theta rhythm is related to the speed of locomotion

Abstract

Hippocampal EEG activity was recorded in rats during locomotion, spontaneous or induced by electrical stimulation of subthalamic locomotor region (SLR) and posterior hypothalamus (PH). Spontaneous locomotion was associated with the theta frequency (6-8.5 Hz). Electrically induced locomotion was also associated with theta rhythm, frequency of which depended on the site of stimulation. Theta frequency during SLR evoked locomotion was almost the same as during spontaneous locomotion (7-9 Hz). PH induced locomotion was accompanied by higher theta frequency (9-11 Hz). Theta frequency and the speed of locomotion were positively correlated during spontaneous locomotion. During electrically induced locomotion the theta frequency was much higher than expected when related to the speed of spontaneous locomotion. The electrically evoked locomotion may result from activation of various systems. Stimulation of the SLR activates system responsible for the exploratory behavior, while stimulation of PH evokes locomotion related to aversive behavior. Thus, we conclude that the theta rhythm frequency may depend not only on the speed of locomotion but also on the rats' motivational-emotional state, associated with locomotion performed by the animal.