Mental exercise wards of dementia in old age

We often hear that the brain is like a muscle – use it or loose it. This piece of common wisdom isn't just an old wives' tale, but grounded in science: a new study suggests that exercising the brain at any age may help you keep your wits in old age, even if telltale signs of the physical damage in the brain are present.

Previous research tells us that engaging in mentally stimulating activities, like reading and writing, slows down and reduces late-life cognitive decline. But how? One theory is that working out your brain muscles somehow creates a “reserve”, buffering against age-related cognitive decline. So remaining intellectually agile is a direct outcome of mental exercise. Another idea is that aging-related tear and wear is the CAUSE of cognitive decline. In other words, loosing mental wittiness is a direct consequence of physical damage. Now the question is: can a book a day preserve cognition in old age, even in lieu of telltale signs of dementia-related brain damage?

Wilson RS et al. 2013 Life-span cognitive activity, neuropathologic burden, and cognitive aging. Neurology.  doi: 10.1212/WNL.0b013e31829c5e8a

Researchers asked roughly 300 elderly participants about how much they engaged in cognitive pursuits in early and late stages of their lives. The activities queried had very low barriers to entry – stuff like reading books, writing letters, visiting a library to look up information - as opposed to more niche brain training exercise programs like Luminosity. The participants then took 19 (!!) standardized tests annually measuring all aspects of their cognition until they passed away, for an average of roughly 6 years. Following death, their brains were examined for neurological abnormalities, such as mirco-strokes, Alzheimer’s disease-related plagues and tangles (pictured below) and Parkinson’s disease-related clumps called Lewy bodies.

Neuropathology in Alzheimer's disease. Source: http://farm5.static.flickr.com/

Unsurprisingly (and unfortunately), 153 people showed clinical signs of cognitive impairment during the follow up sessions, and roughly 68% of participants had visible signs of neuropathic damage at death. It seems reasonable to assume that different amounts of brain damage led to different degrees of cognitive impairment. However, when researchers tested this hypothesis with a mathematical model, these marks of brain damage couldn’t fully explain why people had different rates of cognitive decline.

Researchers then looked at the effect of late-life mental exercise on cognition. As you can see from the graph below, compared to average late-life activity levels (blue line, 50th percentile), frequently reading and/or writing (10th percentile) slowed down mental aging by roughly ~30% (green line), while mental inactivity (90th percentile) sped it up by nearly 49%. This means that not working your brain in late life can increase cognitive decline by almost 1 ½ times. Yikes!

Further analysis showed that frequent cognitive activity in youth and early adulthood (6 -40 years old) also helped delay memory loss and thinking impairments. When researchers looked at early and late life activity together, both were related to change in cognition, but differed in WHICH aspect they affected most. Early-life activity was related to changes in working memory – the ability to hold multiple pieces of information in mind, using them to reason things out or plan the next step of action. Late-life activity, on the other hand, was related not just to working memory, but also to plain-old-“oh here’re my keys” memory and visualspatial ability, ie to mentally manipulate a static 2D-map to find your way home. The benefits of cognitive activity didn’t go away with brain damage: even though the brain may show pathological signs of Alzheimer’s or Parkinson’s, intellectual pursuits still slowed down cognitive decline.

Why does engaging the brain preserve its function in later life? Although it seems like an “oh-duh” question, scientists haven’t pinpointed the reason(s) quite yet. Cognitive activity is associated with changes in the brain’s volume, structure and connectivity, all of which may protect brain regions associated with cognitive functions in later life. As of now, we still know very little about what goes on at the neural circuit and neuronal levels.

Regardless of mechanism, this study is in line with many others that show a lifetime of frequent mental engagement wards off senior moments later in life. You don’t have to be a bookworm or a writer to reap the benefits – learning a second language helps as well.

Last note: The paper reported how often the participants were reading/writing (for the 90th percentile, almost everyday of their lives). It did not say a word about WHAT they were reading, so I’m assuming fiction and nonfiction are fair game. As my lab mate just pondered out loud “I wonder if Fifty Shades of Grey counts too…”

Wilson RS, Boyle PA, Yu L, Barnes LL, Schneider JA, & Bennett DA (2013). Life-span cognitive activity, neuropathologic burden, and cognitive aging. Neurology PMID: 23825173