Brutal Truths About
the Aging Brain
The sad truth is that even normal aging has a devastating effect on our ability to learn and remember, on the speed with which we process information, and on our ability to reason. Recent studies suggest that the total loss in brain volume due to atrophy—a wasting away of tissue caused by cell degeneration—between our teen years and old age is 15 percent or more, which means that by the time we’re in our seventies, our brains have shrunk to the size they were when we were between 2 and 3 years old. Unfortunately, most of the loss is in gray matter, the critically important part of the brain composed of neurons, the cells that transmit the signals that keep us breathing and thinking.
Contrary to what scientists long believed, only about 10 percent of our neurons die during adulthood. The real loss is in the network of connections—the “dendritic trees” that allow a single neuron to be connected to a thousand others. Over the years, 25 percent or more of this network disappears. According to William Jagust, a neuroscientist at the University of California, Berkeley, adults are also losing dopamine, a critical neurotransmitter (the type of chemical involved in transmitting signals between neurons), at the rate of 5 to 8 percent per decade. “By age 80,” Jagust says, “you’ve lost 40 percent or so of dopamine function. When you think about it, it’s remarkable that old people can do so well.”
Shrinkage, dopamine depletion, and lost dendritic connections are not the only problems facing the aging brain. Myelin, a substance that insulates neurons, deteriorates, and the number of nerve fibers that carry messages throughout the central nervous system also decreases. Chemical problems—such as an increase in calcium conductance, which might impair neuronal communication—also become more common in older brains, as do problems with gene expression and protein production.
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