When it comes to the brain, 'more is better' seems like an obvious assumption. But in the case of synapses, which are the connections between brain cells, too many or too few can both disrupt brain function. Researchers recently found an immune-system protein that moonlights in the nervous system to help regulate the number of synapses, and could play an unexpected role in conditions such as Alzheimer's disease, type 2 diabetes and autism.