They first completed questionnaires about their sexual activity over the previous 12 months (never, monthly or weekly) along with other questions about lifestyle habits and health.
Then they took a series of tests to assess memory, attention, language apprehension, verbal fluency and visuospatial ability. All of the tests were standard measures of cognitive ability and processing speed. The visuospatial tests, for example, required participants to draw a clock face from memory (harder than it sounds), among other things.
When the test results were lined up with the sexual activity results, it didn’t appear that having more sex had a direct influence on attention, memory or language. Those who reported having essentially no sex life did just as well as the most active of the group.
But in the categories of verbal fluency and visuospatial ability, distinct differences appeared. Those reporting weekly sexual activity did significantly better on both tests, especially verbal fluency. A typical test of verbal fluency might include a mixed verbal challenge, like naming as many animals as possible and then saying as many words beginning with F as possible. The rapid shift from one verbal challenge to another shows how fluidly the brain can switch verbal tracks while also engaging memory. And for that sort of challenge, this study suggests, more frequent sex is a brain boost.
Why this might be true is another story, and the doors are open for speculation. Health and lifestyle may play a role (this study couldn't rule those factors out entirely), but beyond that there are other reasons to think more sex is good for the brain. The first possible and perhaps most likely explanation is that sex floods neural pathways with chemicals that trigger a range of effects. Most notably, dopamine—the main fuel of the brain’s reward center—plays a major role in learning, and may also exert an octane-boosting effect on certain cognitive capabilities. More frequent sex increases the availability of dopamine in the brain for periods of time, and that may in turn enhance those capabilities. Why some capabilities would be enhanced but not others is an open question.
Another possibility, suggested by earlier research on middle-aged rats, is that frequent sex helps the brain grow new neurons. This process, known as neurogenesis, is vital to the brain’s plasticity—its ongoing ability to adapt and change—and plasticity is now known to occur in certain areas of the adult brain, not just in younger brains. The earlier research suggests that sexual activity serves as a buffer for protecting neuron growth against the effects of stress. This, again, may come down to the connection between sex and the availability of potent neurochemicals like dopamine.
Whatever the explanation, I think we can put these findings in the “good news” file. They aren’t conclusive (and this was a small study) but they build on previous research showing similar results, so it's reasonable to conclude that there's something there worth considering.
The study was published in the Journals of Gerontology, Series B: Psychological and Social Sciences.