Why do our minds slow as we age? Do our neurons just become increasingly lazy? According to Scientific American, it's actually our ability to filter out distractions that becomes impaired over time. At least, so suggests the following study:
Adam Gazzaley of the University of California, San Francisco, and his colleagues asked two groups—one made up of 19- to 33-year-olds and the other of 60- to 72-year-olds—to perform a memory task. The researchers used electroencephalography to record electrical signals from the participants' brains in milliseconds during the task. In contrast to the younger adults, the older group could not suppress distracting stimuli during the first 200 milliseconds after exposure. "At later time points, the ability to ignore does show up," Gazzaley says. "It's not abolished, just delayed." By then, however, the irrelevant information had interfered with the memory task, making the older group less accurate overall than the younger group.
With that said, Gazzaley stresses that "not all older adults are impaired relative to younger adults"—the older subjects just don't do as well on average.