Hippocampal network oscillations: dissecting the septo-hippocampal circuitry

How the brain encodes information. Our brain processes information in a network of nerve cells. The communication between these nerve cells occurs via specialized structures called synapses. When an electrical signal (action potential) travels along the nerve cell and reaches the synapse then a messenger substance is released from the synapse. This messenger substance is received by a receptor protein in the membrane of the adjacent nerve cell. The firing of action potentials of individual nerve cells and the communication between these cells via synapses is very important for the processing of information, but it might not be sufficient. To allow efficient information processing by individual nerve cells, their action potential firing might have to be embedded in a temporal context. Such a 'clock signal' in the brain might be provided by so called network oscillations. These 'brain waves' arise from voltage changes in the extracellular space of the brain, which are caused by the ion flux that is associated with synchronous activity of large groups of nerve cells. Using electrodes that are inserted into the brain these waves can be measured. It was found that there are different types of brain waves and that each of them is associated with a particular behaviour in an animal. The hippocampus is a brain structure which is important for learning and memory. Here different brain waves are hypothesised to be necessary for the encoding of information in different phases of memory formation. However it has not been possible to directly test this. In the experiments I propose in this application I want to test the function of brain waves in memory formation. We have developed a new technique that allows us to interfere with selected synapses and thus with communication between selected nerve cells that are important for the generation of different types of brain waves. By interfering with nerve cell communication in different parts of the nerve cell network we want to find out which parts of the network generate which type of brain waves. Once we have this information we will selectively disrupt distinct types of brain waves and test how this influences learning and memory.