There is now a growing appreciation of cross-talk between the nervous and immune systems. Here, Ribeiro et al. report that interleukin-17 (IL-17)–producing γδ T cells that arise early in life and home to the meninges of neonatal mice play an essential role in the development of short-term memories. Both mice lacking γδ T cells and IL-17 show impaired performance in Y-maze tests that rely on short-term memory but did not show any deficits in other behavioral tests, including tests that gauge long-term memory. The authors found that meningeal IL-17–producing γδ T cells promote secretion of brain-derived neurotropic factor in mouse brains. Further studies are needed to understand the local and systemic effects of IL-17 on neuronal and non-neuronal cells in the brain.