FUNCTIONS FOR INTERNEURONAL NETS IN THE HIPPOCAMPUS

Recent advances in the physiology of hippocampal interneurons are summ arized in this article. These findings suggest that through their inte rconnectivity inhibitory interneurons can maintain large-scale oscilla tions at various frequency ranges (theta, gamma, and 200-Hz bands). We suggest that networks of inhibitory interneurons within the forebrain impose coordinated oscillatory ''contexts'' for the ''content'' carri ed by networks of principal cells. These oscillating inhibitory networ ks may provide the precise temporal structure necessary for ensembles of neurons to perform. specific functions, such as memory trace format ion and retrieval. In addition, synaptic inhibition is shown to reduce the somadendritic backpropagation of sodium spikes and to prevent the occurrence of calcium spikes in dendrites. These observations indicat e that interneurons are in an excellent position to control neuronal p lasticity and allow synaptic transmission either with or without long- term modification of synaptic strength.