The human brain is packed with star-shaped cells called astrocytes; they make up about 50 percent of cells in the cerebral cortex, and far outnumber the neurons that process and transmit information. Yet until recently, researchers thought these ubiquitous brain cells were fairly unimportant to the brain’s functioning. Now a new study rebuts that theory, and indicates that astrocytes play a major role in sending blood to areas of brain activity.
In the study, a team of MIT researchers peered into the visual cortex of live ferrets with an advanced microscope to watch how the brain cells responded to visual stimuli. “Electrically, astrocytes are pretty silent,” study co-author James Schummers said…. “A lot of what we know about neurons is from sticking electrodes in them. We couldn’t record from astrocytes, so we ignored them.” The researchers changed this perception by imaging astrocytes with two-photon microscopy. “The first thing we noticed was that the astrocytes were responding to visual stimuli. That took us completely by surprise,” Schummers said. “We didn’t expect them to do anything at all. Yet there they were, blinking just like neurons were blinking” [HealthDay News].
Evolutionary biologists have long been interested in the dimensions of the human noggin, and more specifically the size of the brain tucked inside. The human cranium is so big, they point out, that it poses risks during childbirth, and it takes a lot of energy to keep that big brain humming along. Most researchers assumed that the large size must deliver a major evolutionary advantage, like the capacity for increased intelligence, to make up for these disadvantages.
Now a study published in Nature Neuroscience [subscription required] suggests that it wasn’t an increased number of brain cells that gave humans such an evolutionary boost, but rather the increased complexity in the synapses between brain cells.