Enhanced hippocampal theta EEG during whole body rotations in awake restrained rats

Hippocampal slow wave activity in the theta band was studied in awake restrained rats as they were rotated in the horizontal plane both in light and in darkness. Monopolar recordings were made with an insulated silver wire (200 microns diameter) implanted in the dentate gyrus with reference to the occipital bone. Fast Fourier transforms were made of data recorded when the rat was either rotated passively or remained immobile. The power in the 6-9 Hz frequency band ('type I' theta) was significantly increased during rotations. The same results were obtained in experiments performed in the light or in complete darkness. These results provide evidence for a role of inertial (possibly, vestibular) information in hippocampal spatial representations.