What have scientists learn about glia cells through recent research?

The current issue of the journal Science (November 5) marks a turning point in research on the brain. This event is fascinating not only for the wealth of new information about how the brain functions and how it fails in mental and neurological illness, but equally as a rare display of a field of science changing course. Such transitions are the lore of scientific history, but rarely do we have the opportunity to witness such pivotal moments in real time.

The journal Science is a premier international journal covering all areas of science, and this issue contains a special section on glia. Glia, in contrast to neurons, are brain cells that do not generate electrical impulses, and there are a lot of them—85 percent of the cells in the brain. Yet, these cells have been largely neglected for 100 years. I call this new frontier of neuroscience "The Other Brain," because we are only now beginning to explore it. The new findings are expanding our concept of information processing in the brain. They are leading rapidly to new treatments for diseases ranging from spinal cord injury to brain cancer to chronic pain, and Alzheimer's disease. And they are overturning a century of conventional thinking about how the brain operates at the most fundamental level. 

In the past, glia were understood to support neurons; to feed them and clean up after them, and to respond to brain injury. But these functions were regarded as peripheral to the exciting functions that neurons perform in processing information and storing memories. Consequently, research on glia did not fare well in the fierce competition for the limited grant funding for brain research. Neuroscientists were not trained in glial science, and the standard texts cover glia superficially, if at all. Editors at major journals were not well versed in these odd and very complicated brain cells. As a consequence, glial research was rarely published in high-impact scientific journals. These forces dragged on glial researchers for decades. Now all of this is changing.

The functions of glia can be broadly divided into three main categories, and four very different types of glia serve these different functions. Astrocytes, glia so named because their shape reminded early anatomists of stars, fill the spaces between neurons. Astrocytes provide the energy source to neurons; they maintain the chemical environment surrounding neurons within the narrow limits required for neurons to survive and fire electrical impulses, and to communicate at synapses.

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