The diverse functions of our nervous system depend on the precise interconnections of millions of neurons. These connections are made during embryonic and postnatal development, and are constantly modified by learning, memory and experience. Many neurodevelopmental diseases and psychiatric disorders are the results of defects in the initial assembly of neuronal connections. Laboratories in our department are using a variety of approaches and animal models to study the genes that regulate these processes in order to find new ways to repair diseased or damaged neurons and connections in the human brain and spinal cord. Their studies have identified factors that control the diversity and survival of neurons, specify precise neuronal connections, regulate the formation of synapses, and contribute to activity-dependent synaptic plasticity.