22 June 2019 | New Scientist | 41It is a harsh fact of life: as you get older,
your cognitive abilities start to wane.
But why is it that some people reach
a ripe old age with little more than the
odd “senior moment”, while others
have far greater mental decline?
The brain starts shrinking around
the age of 40, with cells deteriorating
most quickly in the frontal lobe, the
striatum and the hippocampus – areas
involved in our most complex thoughts,
movement and memory. How resistant
you are to the effects of this decline
is likely to be associated with your
cognitive reserve. This is a kind of
mental buffer that allows your brain
to sustain more damage before you
notice changes in your cognition.
Cognitive reserve isn’t just down to
someone having more neurons than
another person, but also to how well
their neurons engage with each other
across different networks in the brain.
This allows the brain to compensate
when age-related decline occurs or
disease takes hold, and helps reroute
information so that the organ can
continue to work optimally. It is a bit
like boosting the processing power
in a computer: more things can gowrong before you start to notice it
slowing down.
Our environment can also influence
cognitive reserve. A high level of
education offers one of the biggest
boosts, whereas obesity and insulin
resistance seem to reduce it. Several
genes also help us resist cognitive
decline. Tiny genetic variations are
associated with our susceptibility to
Alzheimer’s as well as with how the
brain utilises energy reserves and
reacts to injury and pathogens.Exercise the mind
Brain shrinkage over time sounds bleak,
but there is some good news. Although
most of our brain cells are created soon
after birth, we can make certain types of
neuron even into our 90s. This ability
might go some way in explaining why
some people’s brains fare better against
the ravages of old age.
There are a few other ways to boost
cognitive reserve. Continuing to
educate yourself throughout your life
appears to provide one of the biggest
benefits, but playing a musical
instrument, socialising, getting the
right amount of sleep and speaking
more than one language also help.
Don’t put your feet up for too long
though: the adage “healthy body,
healthy mind” turns out to be true.
“If you’re looking to maintain brain
health, you need to exercise,” says
Steve Harridge, director of the Centre
for Human and Applied Physiological
Sciences at King’s College London.
Regular workouts bring about
significant improvements in memory,
attention, processing speed and
executive functions, such as planning
and multitasking.
And don’t leave it too late. Richard
Henson at the University of Cambridge
and his colleagues have discovered that
the things we do in midlife – outside of
work and education – make a unique
contribution to brain health in older
age. The activities retirees do in their old
age, however, had less impact. “Midlife
seems to be a good time to intervene, to
nudge people into taking part in more
activities – physical, intellectual and
social – that might bode well for them
20 or 30 years later,” says Henson. ❚
Helen ThomsonWhat makes some brains more
resistant to decline?researchers identified a new type
of brain cell, dubbed a rosehip
neuron due to its resemblance
to the shape of a rosebush fruit.
It may only exist in humans.
Other secrets may well be
revealed by Lein’s ongoing efforts
to create a map of all the brain’s cell
types, painstaking detective work
that looks at the genes single cells
express. He has recently studied
the neocortex – the outer part of the
human brain that deals with higher
processes and makes up 80 per cent
of its mass – and found 75 different
types of cells there alone.
Joshua Howgego
Mind reading:
new technology
gives us an
unprecedented
view of the
brain in actionBeta brainwavesOf all primates’
brains, those of
humans have
the foldiest
outer layerK.HFUNG/SCIENCE
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