The brain, and the rest of the nervous system, consists of nerve cells (neurons) and non-neuronal cells (glial cells), which by far outnumber the neurons, but in the past have received much less attention.

This began to change about 30 years ago with the realization that glial cells carry out very important functions, generally in collaboration with the nerve cells. Evidence is now starting to accumulate that glial cells, especially astrocytes and microglia, may be major (in some cases the main) players in a multitude of neurological and mental diseases, and that different types of...