Microglia, the immune cells of the brain, are known for eating up unwanted items like germs and debris, much as their counterparts do in the rest of the body. In early childhood, certain microglia remove unneeded connections, or synapses, to shape the adult brain’s organized circuitry. Now, Cold Spring Harbor Laboratory (CSHL) Professor Linda Van Aelst has found that in mice, microglia also help neurons grow synapses critical to cognitive functioning.