Excitatory Synapses and Brain Function. Perhaps no other structure is more fundamental to our understanding of the brain than the synapse. In the central nervous system, excitatory synapses represent the primary source of information communication between neurons, whether for local interactions within circuits or for linking discrete regions of the brain. One of the most extraordinary properties of excitatory synapses is the ability to under activity-dependent long-lasting changes in synaptic strength, providing the most compelling cellular model for learning and memory. Synapses also serve as the site of action for many commonly prescribed medications and synaptic disruption contributes to many neurological and psychiatric disorders. These include schizophrenia, autism, depression, substance abuse and addiction, Parkinson’s disease, Alzheimer’s disease, traumatic brain injury, stroke and epilepsy. In some cases, synaptic dysfunction is causal in disease, whereas in other cases it represents the downstream sequelae of one or more underlying molecular defects. In either case, a fundamental understanding of the formation, structure, molecular organization, signaling function, and plasticity of synapses is essential to achieving progress in lessening the burden of human neurological disease and for predicting and improving mental health.