In this animation, we focus on the brain’s neural development in a baby. The thymus releases cells, which travel along the bloodstream to the brain. The microglia interact with these cells and become activated, changing morphology from circular cells to extended spider-like shapes. These tentacles then wrap around synapses, pruning some of the connections between neurons. This gives fewer but stronger connections between neurons, and is part of the process of forming memories and the maturation of the brain.