The brain is an extremely complex network, consisting of billions of neurons connected by trillions of synapses. The details of these connections-which neurons form synaptic connections with which other neurons-are crucial in determining brain function. Malformation of these connections during prenatal and early postnatal development can lead to mental retardation, autism or schizophrenia; loss of specific connections later in life is associated with neurodegenerative diseases such as Alzheimer's. Researchers in this study are developing a method for identifying these complex neuronal connections in animal models of disease. Using high-throughput DNA sequencing, researchers will probe the connectivity of neural circuits at single-neuron resolution. This novel, efficient method for determining the brain's wiring diagram could transform neuroscience research and have a profound impact on understanding the causes of neurodevelopmental and neurodegenerative diseases.