State of Activity in the Hippocampus Follows Pupil Diameter
The rate of sharp-wave ripples in the hippocampus is highly correlated with pupil diameter. As pupil becomes larger, indicating an increase in arousal, sharp-wave ripples decrease in their rate of occurrence. When the mouse walks, the pupil dilates, and sharp wave ripples decrease dramatically. We found a very high inverse correlation between the state of the hippocampus (and brain) with pupil diameter. Thus pupil diameter is a useful tool to determine the state of the brain.