So how does one stimulate neurogenesis? Scientists do not have all the answers, but studies of older people who have maintained their mental acuity provide some clues. They tend to be socially connected, with strong ties to relatives, friends and community. They are often both physically healthy and physically active. And they tend to be engaged in stimulating or intellectually challenging activities.

The big question is whether they remain mentally alert because they engage in these activities, or whether they are able to engage in these activities because they are cognitively intact.

“We don’t know whether this is an example of reverse causation or not - it’s probably a two-way street,” said Bruce S McEwen, who heads the neuroendocrinology lab at Rockefeller University in New York.

But some interventional studies that have introduced older adults to exercise regimens have reported remarkable results.

Researchers at the University of Illinois at Urbana-Champaign recruited a group of sedentary adults between the ages of 60 and 75, assigning half of them to an aerobic exercise programme that met three times a week to walk, while a control group did anaerobic stretching and toning.

The scientists measured the group’s cognitive function before and after the six-month programme and found improvements among those who had done the walking.

“Six months of exercise will buy you a 15 to 20 per cent improvement in memory, decision-making ability and attention,” said Arthur F Kramer, a professor of psychology at the University of Illinois. “It will also buy you increases in the volume of various brain regions in the prefrontal and temporal cortex, and more efficient neuronetworks that support the kind of cognition we examined.”

... contd.