Ever since their discovery more than 150 years ago, glial cells have been defined by what they couldn't do. Above all, they have lacked the ability to communicate with other cells through fast electrical and chemical signals--action potentials running down axons and transmitter release at synapses. This has been the exclusive property of neurons, their arch rivals in the battle for researchers' attention--and funding. And because action potentials remain the dominant currency of information processing in the brain, most neuroscientists still see glia as second-class supporting material--the brain's' glue'.

But sure enough, each year brings further exceptions to such a strict division of labour. In 2008, for example, a subclass of glial cell was reported to fire bona fide action potentials. And a sizeable fraction of the glial research community entertains the radical view that evoked release of neurotransmitters by glial cells--'gliotransmission'--must contribute to the information-processing power of the brain (see News Feature, page 160).