One of the first things you’ll learn about if you start studying the brain is that it is made of cells called neurons. While neuroscientists have a decent understanding about how neurons work, it turns out that at least half of the brain is actually made of non-neuronal cells called glia*. Glia, named based on the Greek word for ‘glue,’ were initially thought to be a type of connective tissue in the nervous system, acting just as scaffolding, while the neurons did all the communicating. In the last couple decades, the growing field of neuroimmunology has highlighted the importance of a certain kind of glia: microglia, the brain’s resident immune cells.