Multiple Rhythms and Switches in the Nervous System

Networks of neurons in the nervous system can produce a variety of temporal patterns of different frequency; the same network can produce different rhythms at different times, or several rhythms at one time. We focus here on the gamma (30-90 Hz) and theta (4-12 Hz) rhythms produced in the hippocampus, a part of the nervous system critical for learning and recall. We discuss experiments and models that suggest that there are separate subnetworks that produce the different rhythms; the sharing of components of the networks induces competition between the rhythms, which can lead to suppression of one of the rhythms, or nesting of the rhythms. We show how low-dimensional maps can help to understand the properties of the cells and networks to allow this to happen.