Researchers have revealed that microglia -- cells involved in immune functions in the brain -- also influence brain connectivity and formation of new links between neurons in the developing brain. By directly contacting dendrites, they cause accumulation of Ca2+ and actin, leading to establishment of projections called filopodia. Filopodia then extend and seek out presynaptic terminals of other neurons, to create new synapses that form the basis of neuronal communication.