Why do we lose cognitive ability as we age?

About two-thirds of Americans experience at least some cognitive impairment by the time they reach age 70. In New Hampshire, where the population is the second oldest in the United States, age related illness is a particularly salient public health issue. Recent research from Adam Brockett, assistant professor of biological sciences, clarifies part of this neuroscience puzzle by revealing that two different types of cognitive abilities — those acquired through lifelong experiences and those developed to adapt to new information — exhibit different levels of decline as we age.

“Research has suggested that what’s called ‘crystallized intelligence,’ a base of information gained with experience throughout life, is well maintained,” says Brockett, whose research was published in the journal Frontiers in Aging Neuroscience. “‘Fluid intelligence,’ which involves quickly processing and adapting to new information or changes in circumstances, tends to be what is lost over time. To stop or delay impairment, you need to know which neural processes are changing and which are holding steady.”

The results of the study, which looked at rats’ performance of cognitive tasks, support the earlier research finding that aging does not affect different neural processes in the same way. The rats performed progressively worse with age on the test that demanded rapid behavioral adaptation and fluid intelligence. Performance on the test involving self-control and crystallized intelligence, however, remained consistent.

The researchers also hypothesized that any observable changes in cognitive function likely began far earlier, at the molecular level. They found that rats with high levels of a protein called a histone deacetylase, which shuts down some genes and has been found at high levels in the brains of some people with cognitive impairment, did slightly worse on the fluid intelligence test, suggesting that reduced gene activity in brain neurons may play a role in losing full cognitive function.

As our population ages, the need to help older adults stay mentally sharp grows more urgent. Understanding how neurological functions change over time is critical to helping scientists develop effective strategies and interventions that will help them do just that.