Relationship between hippocampal theta-wave frequency and emotional behaviors in rabbits produced with stresses or psychotropic drugs.

The hippocampal EEG power spectra of rabbits were analyzed to clarify the relationship between the theta-wave and emotionality. The relative power of T2 (6.0-7.9 Hz)/T1 (4.0-5.9 Hz) represented the index of theta-wave change. Emotional excitement (produced with novelty stress or methamphetamine) or suppression (produced with restraint stress or reserpine) increased or decreased T2/T1 ratios within around +/- 1 Hz changes. Furthermore, the imaging patterns of the peak feature make possible detailed characterization of emotional states. These results suggest that the hippocampus finely adjusts the theta-wave on a +/- 1 Hz level, with a fine balance of voltage, in response to the emotional activity.