A Different View of Aging


by Brenda Patoine

January, 2006

True or false: You lose about 10,000 neurons a day as you age.

The answer: False. Neuroscientists discounted this myth years ago, yet somehow it endures, conjuring images of our brains slowly shrinking with each memory slip.

This is one myth you can forget. The current message from the neuroscience of aging focuses instead on cognitive maintenance, and there is encouraging news from people who are doing it well.

“A different picture of aging has emerged,” said Paul Coleman, a neurobiologist at the University of Rochester, during the neuroscience meeting. Replacing the old “aging equals cognitive decline” equation is a new understanding of the remarkable variability in brain aging among individuals. Clearly, some people age more “successfully” than others. While there are measurable biological and chemical changes that can occur in the aging brain and dull cognitive sharpness, it is by no means predetermined that this will occur in any one of us.

The genes we were dealt at birth surely play a role. Longevity runs in families, and studies of twins show that about half of the variance in memory abilities is inherited.

“Genetics can explain part but not all of the variance among individuals,” said Marilyn Albert, a Johns Hopkins neuropsychologist who spoke about the aging brain in the public lecture at the conference. “So there must be additional factors that play a role.”

Since the late 1980s, researchers have systematically studied older adults to try to identify variations in lifestyle that predict successful cognitive maintenance. Two decades and 15,000 people later, the consensus boils down to a few fundamental tenets: be physically and mentally active, stay socially engaged, and reduce risk factors that can cause vascular problems (such as hypertension and high cholesterol).

“It’s clear there are multiple factors that predict cognitive maintenance, and it is very likely that a combination of these factors is more important than any one,” Albert said. This recognition has tremendous implications for designing intervention programs that tackle each piece of the pie in some way, incorporating physical exercise, intellectual stimulation, or social engagement. Albert’s prescription for the perfect activity that combines all of these elements: shop-ping.

Although no one has yet studied the cognitive benefits of shopping, there is growing evidence that dancing may pack a triple punch. A new study reported at the conference revealed that older adults who learned Argentine tango dancing experienced improvements in cognition and day-to-day task performance. Tango, said study author Patricia McKinley of McGill University, combines social integration (dancing with a partner; participating in a group class) with mental challenge (learning complicated dance steps) and physical exercise requiring balance and coordination. This study extends previous published reports that have linked dance practice or group dance lessons to improved cognitive skills.

Unraveling the ‘Why’

Given the evidence that mental and physical exercise and social interaction make a difference to your brain, the question is why. How do these lifestyle traits translate into better brain health? How do risk factors traditionally associated with heart disease put the brain at risk? Recent studies in laboratory animals have helped identify possible underlying mechanisms.

For example, rodent studies have shown that exercise stimulates the brain’s production of a biochemical called brain-derived neurotrophic factor, or BDNF, and switches on BDNF-producing genes in the hippocampus, part of the brain’s short-term memory center. BDNF is one of a family of biochemicals that nourish and support neurons, and it is known to play a role in synaptic plasticity, the reshaping of nerve connections that occurs with learning and experience.

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A woman learns tango from her partner, an instructor, as part of a recent study. This study reinforced findings that dancing helps older people remain cognitively strong via a mix of social, mental, and physical stimulation. Image courtesy of Patricia McKinley, McGill School of Physical and Occupational Therapy

Higher BDNF levels also are linked to increased neurogenesis (new nerve cell generation) in the hippocampus. In humans, a recent brain imaging study by Art Kramer at the University of Illinois-Champaign found that older adults who participated in a group exercise class had increased activity in the hippocampus.

Albert said there is increasing evidence that mental activity may con-tribute to brain health via similar mechanisms: enhancing synaptic plasticity, boosting neurogenesis, and turning on certain genes.

It is possible that the combination of these effects, as well as others still unknown, contributes to a more adaptable brain that can more readily alter its nerve synapses and develop alternative processing pathways. This flexibility could enable the brain to compensate for any age-related physiological changes that might occur. Evidence for this hypothesis comes from brain imaging studies in which older adults who perform well on memory tests had distinct patterns of brain activity when processing the tasks, patterns that differ from those in younger people.

The mechanisms by which social engagement benefits the brain are less clear, but Albert suspects that the critical link may be stress reduction— or, more specifically, a reduction in the level of stress hormones, which are known to damage neurons in the hippocampus. She said people who are socially active and regularly interact with other people for fun and pleasure also tend to have greater feelings of self-efficacy, the attitude that “I make a difference.” These traits may bolster one’s capacity to manage stress, which would spare the hippocampus from being battered by glucocorticoids and other stress hormones toxic to neurons.

Vascular risk factors, such as high blood pressure, diabetes, high cholesterol, obesity, and smoking, may be bad for the brain for the same reasons they are bad for the heart: they dam-age or weaken arteries, through various mechanisms. Each of these can increase the risk of stroke and vascular dementia, and, as is the case in heart disease, their negative effects may be additive.

Enrich Your Brain

Taken as a whole, the advice from neuroscience might be boiled down to this: enrich your life. Science has revealed over and over that environ-mental complexity is a very good thing for the brain.

Science has revealed over and over that environmental complexity is a very good thing for the brain.

A large and rapidly growing body of evidence shows that rodents that are raised in cages with plenty of toys, tunnels, and running wheels perform better on various learning tests, and the effects seem to be long-lasting. Older animals reared this way can even beat out younger animals raised normally. Separate research teams have reported increased rates of neurogenesis in the hippocampus and increased levels of certain nerve growth factors in the brains of animals living in complex environments. Such environments may even help slow the progression of Alzheimer’s by lowering levels of beta-amyloid, the characteristic protein in the disease.

Like tango or shopping, these toy-filled cages offer their four-legged inhabitants physical activity, mental stimulation, and social interaction (with other animals). While scientists continue to sort out the relative contributions of each component and precisely how they change the brain, the best advice from neuroscience for keeping your brain healthy is still: use it, in every way possible.