For decades, glia were considered merely support cells for neurons. By the 1990s, it was suggested that glial cells partake in bidirectional communication with neurons. In 1999, the Haydon lab’s review on the tripartite synapse suggested that astrocytes – the most abundant glial cell in the brain – play an integral part in modulating synaptic activity. When cultured astrocytes are stimulated with a micropipette, their intracellular calcium levels increase. Using local electrical stimuli, it was demonstrated that astrocytes are able to signal to adjacent neurons. After the demonstration of Ca2+- dependent glutamate release from astrocytes, it was shown that these elevations in calcium concentrations in cultured astrocytes all increased neuronal calcium levels.