The beneficial effects of physical and mental exercise on brain health are already well established. A new American study has helped further pinpoint the impact of these two forms of exercise on the brains of aging adults. Aerobic exercise was found to improve memory, in particular, while cognitive brain training improved executive function.

Previous studies have established that aerobic exercise -- such as walking, swimming or jogging -- helps protect the brain against the effects of aging. This new study, from researchers at the University of Texas at Dallas, USA, has found that physical activity alone is not enough to take care of the brain, as aerobic training principally benefits the memory.

According to the research, physical exercise should be paired with regular mental exercise to stimulate cognitive functions such as decision-making, synthesizing information and perspective-taking.

The scientists studied a group of 36 adults aged between 56 and 65 years old. Participants were split into two groups. The first group took part in a physical training program of activities such as brisk walking and cycling with five-minute warm-up and cool-down sessions. They exercised for three hours a week for three months.

The second group followed a mental training program, again for three hours a week for three months, with exercises working their attention and prioritization skills, their abilities to synthesize information, as well as perspective-taking and problem-solving skills.

The scientists used MRI scans to evaluate brain blood flow in the participants at the beginning and at the end of the study.

They found that brain blood flow was notably higher in participants in the mental training group, with an increase in global brain blood flow of up to 8% compared with participants in the physical training group. "We can lose one to two percent in global brain blood flow every decade, starting in our 20s," said Dr Sandra Bond Chapman, the study's lead author. "To see almost an 8 percent increase in brain blood flow in the cognitive training group may be seen as regaining decades of brain health since blood flow is linked to neural health."

The researchers suggest that staying focused on a goal during reasoning-training exercises triggered neural plasticity, unlike physical training.

The physical training group did, however, show increased blood flow in the bilateral hippocampi, a part of the brain key to memory function that's particularly vulnerable to aging and dementia.

In conclusion, the scientists recommend both mental and physical training to boost brain health and protect the brain from the effects of aging.