Neurons are the nerve cells known to be key players in the brain’s circuitry that enable us to perceive, sense, think, remember and behave. They respond to sensory stimuli and process and transmit electrical pulses through the central nervous system by connecting to each other, forming vast networks in the brain. Lesser known cells in the brain called glial cells, though 10 times more numerous, have been thought to primarily support and protect neurons. But newly published research by a team of neuroscientists at the Salk Institute for Biological Studies in California, including Xin Wang, Ph.D., 2012 NARSAD Young Investigator Grantee, demonstrates that astrocytes, a common type of glial cell, are in fact “essential contributors to information processing and cognitive behavior.”
The team’s findings were reported online July 28th in Proceedings of the National Academy of Sciences. Their key experiment involved treating genetically engineered mice with a chemical that, in a reversible way, disabled the release of chemicals from astrocytes, effectively eliminating the cells' ability to communicate with neighboring cells, but kept communications among neurons intact. The researchers then triggered and measured electrical activity in the mouse brains via electroencephalography, or EEG.
The team targeted what are called gamma waves, known to be important for higher-level brain function; disturbances in these waves have been linked to schizophrenia, Alzheimer's disease, autism, epilepsy and other disorders. They found that in the animals' brains with the "disabled" astrocytes, shorter and weaker gamma waves were produced and the animals showed evidence of cognitive impairment even though their neurons continued to function normally.
In what is called a “novel object recognition” test, mice are given two objects to become familiar with, and then one of the two is replaced by a new object. Healthy mice will invariably spend more time examining the new object in the new pairing, because they already recognize the one included in the first part of the test. But the mice with the disabled astrocytes in this experiment treated all objects the same, whether they were familiar or “novel.”
The researchers report that this new evidence suggests that astrocytes are essential for gamma waves to occur, which in turn enables the brain to learn and change the strength of its neuronal connections. They explain that the recognition system utilized to differentiate between familiar and novel is “hugely important.” That function enables us to recognize other people, places, facts and things that happened in the past.