During periods of restfulness, after the animal has stopped exploring (even briefly), there occur irregular bursts of population activity that give rise to brief but intense high-frequency (100-250 Hz) oscillations in the CA1 pyramidal cell layer. The population activity that happens during the ripples is highly structured and is a major focus of our research. It also reflects the coordinated rhythmic activity of populations of interneurons, which result in the observed “ripple” oscillations in the CA1 pyramidal layer local field potential.
The firing pattern of pyramidal neurons during these population bursts reflects the temporal structure of firing during experience. The observed sequences follow the behavior in forward, as well as in reverse.