Contribution of visual feedback to the hippocampal theta activity in mice

In the hippocampus of rodents, rhythmic electroencephalographic (EEG) activity at 4-12 Hz (theta activity) is observed when the animal is running. Although it has been reported that the theta activity is modulated by various sensory stimuli, the contribution of the visual feedback has not fully understood. In this study, we analyzed the relationship between the locomotion speed and the hippocampal theta activity of freely behaving mice in a virtual environment. It was found that the frequency and the amplitude of the theta activity were correlated with the locomotion speed of the mouse in the virtual space as well as in the real open field. When the visual feedback was switched-off, the frequency and the amplitude of the theta activity were slightly decreased without changing the proportionality constant of the locomotion speed. These data indicate the contribution of the visual feedback to the hippocampal theta activity.