The short of it is, moderate weight training two times per week, can help maintain the smooth flow of information from one portion of your brain to another. And, if your various brain functions can't work together, there are a bunch of issues that can arise. The smooth flow if caused by the reduction of lesion's in the brain's white matter.
A lesion is "damage" such a wound, ulcer, tumor, abscess, etc.
White mater is the high-speed rail system from one portion of your brain to another (the grey matter).See this story for more details http://blogs.biomedcentral.com/on-biology/2014/03/14/the-subway-of-the-brain-why-white-matter-matters/
Teresa Liu-Ambrose - a professor of physical therapy and director of the Aging, Mobility, and Cognitive Neuroscience Laboratory at the University of British Columbia in Vancouver (see http://cogmob.rehab.med.ubc.ca/people) – has published that aerobic exercise had been shown to reduce lesions in the brain's white matter. The study was published October 12 in the Journal of the American Geriatrics Society is called "Resistance Training and White Matter Lesion Progression in Older Women: Exploratory Analysis of a 12-Month Randomized Controlled Trial" – you can see it here http://onlinelibrary.wiley.com/doi/10.1111/jgs.13644/full
The researchers recruited 155 women between the ages of 65 and 75 whose brains showed evidence of white matter lesions via an MRI scan. They were divided into three groups.
One group did resistance training, including moderate weight lifting, once a week. A second group did the resistance training twice a week, and the third group performed a twice-weekly "balance and tone" routine. The exercise sessions continued for a full year.
At the end of the period, the researchers found that all of the groups showed some new lesions. But the women who exercised twice a week had significantly less shrinkage and shredding of their white matter than the group that exercised just once a week. They also walked with more assurance and speed than the women in the other groups.
There was no significant difference between the balance-and-tone exercisers and the once-a-week resistance group.
Liu-Ambrose tells The Times that the findings suggest that weight training can change the structure of the brain for the better, but "a minimum threshold of exercise needs to be achieved," she says.
In other words, once a week in the gym probably isn't enough - at least twice seems to be the key.
Weightlifting, for a stronger body and mind!