The five ages of the brain: Adulthood

The slippery slope

by Graham Lawton

So you're in your early 20s and your brain has finally reached adulthood. Enjoy it while it lasts. The peak of your brain's powers comes at around age 22 and lasts for just half a decade. From there it's downhill all the way.

The peak of your brain's powers comes at age 22 and lasts for just half a decade

This long, slow decline begins at about 27 and runs throughout adulthood, although different abilities decline at different rates. Curiously, the ones that start to go first - those involved with executive control, such as planning and task coordination - are the ones that took the longest to appear during your teens. These abilities are associated with the prefrontal and temporal cortices, which are still maturing well into your early 20s.

Episodic memory, which is involved in recalling events, also declines rapidly, while the brain's processing speed slows down and working memory is able to store less information.

So just how fast is the decline? According to research by Art Kramer, a psychologist at the University of Illinois in Urbana-Champaign, and others, from our mid-20s we lose up to 1 point per decade on a test called the mini mental state examination (see graph). This is a 30-point test of arithmetic, language and basic motor skills that is typically used to assess how fast people with dementia are declining. A 3 to 4 point drop is considered clinically significant. In other words, the decline people typically experience between 25 and 65 has real-world consequences.

That all sounds rather depressing, but there is an upside. The abilities that decline in adulthood rely on "fluid intelligence" - the underlying processing speed of your brain. But so-called "crystallised intelligence", which is roughly equivalent to wisdom, heads in the other direction. So even as your fluid intelligence sags, along with your face and your bottom, your crystallised intelligence keeps growing along with your waistline. The two appear to cancel each other out, at least until we reach our 60s and 70s (see "The five ages of the brain: 5 Old age").

There's another reason to be cheerful. Staying mentally and physically active, eating a decent diet and avoiding cigarettes, booze and mind-altering drugs seem to slow down the inevitable decline. And if it is too late to live the clean life, don't panic. You still have one more chance to turn it around.