Discrete place fields of hippocampal formation interneurons.

The spike discharge of hippocampal excitatory principal cells, also called "place cells," is highly location specific, but the discharge of local inhibitory interneurons is thought to display relatively low spatial specificity. Whereas in other brain regions, such as sensory neocortex, the activity of interneurons is often exquisitely stimulus selective and directly determines the responses of neighboring excitatory neurons, the activity of hippocampal interneurons typically lacks the requisite specificity needed to shape the defined structure of principal cell fields. Here we show that hippocampal formation interneurons have "on" fields (abrupt increases in activity) and "off" fields (abrupt decreases in activity) that are associated with the same location-specific informational content, spatial resolution, and dependency on context as the "place fields" of CA1 principal cells. This establishes that interneurons have well-defined place fields, thus having important implications for understanding how the hippocampus represents spatial information.