The human brain has roughly 10 billion neurons that communicate with one another through synaptic connections.Each neuron is capable of making 5,000-10,000 synapses its targets,leading to 50-100 trillion synaptic connections in the brain.The connections between neurons give rise to functional neural networks that provide the cellular substrate for higher cognitive functions such as learning,memory and,ultimately,consciousness.How these complex connections are established during the early phases of nervous system development and optimized in lifespan remains largely unknown.Continuing our inquiries into the regulation of the relationships among neurons and among synapses within a single neuron,we are increasing our understanding of the conditions necessary to maximize the efficacy of these relationships,and thus to optimize the performance of neural networks.