Hi there and thanks so much for posting this question! Yes we dont know right now what produces what but what most of the research is showing is that aerobic exercise prevents from cognitive impairment-Take a look at this study! http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3056436/
and look at this! Alzheimer's research: Aerobic exercise can protect brain, improve mental agility http://www.oregonlive.com/health/index.ssf/2010/01/aerobic_training_boosts_aging.html
In either case I wanted to share with you my research with one of the top experts in the brain and aerobic exercise please take a look
What is the goal of the Neurocognitive Kiniesology Laboratory?
The goal of the NCKLab is to promote better brain health and effective cognitive function. Our focus has been on the examination of health-related behaviors, such as exercise and fitness, and changes in cognitive health and effective functioning. Future work will examine other health factors such as body composition and diet.
> Your lab recently was awarded a grant to study physical activity and cognitive function in pre-adolescents. Could you tell us a little bit more about this exciting trial?
Our website is a bit dated. The grant was awarded about a year ago. My students and I have been awarded several grants. All have the same purpose: to authenticate the link between physical activity and cognitive health. The grant listed on my website was awarded to develop a randomized control trial to examine the effect of an after-school physical activity program on cognitive and brain health.
> In your article : “Be smart : Exercise your heart - exercise effects on brain cognition” - your premise is that exercise can make us smarter. Were you surprised by the results of your research that led to these conclusions?
Not at all! There were several researchers before me who had dabbled in this area, providing me with a small literature to formulate my hypotheses. Further, my work fits within the theoretical views of Dr. Frank Booth and Dr. Fernando Gomez-Panilla, both of whom suggest an evolutionary link between physical activity and brain health. They work independent to one another, but have similar ideas in that they both suggest that our ancestry included genetic programming for physical activity. After all, our hunter-gatherer ancestors needed to be mobile and use both brain and body to capture food. Stated another way, they had to spend energy to make energy. Despite the fact that our genetic programming has not changed, our behaviors have and we (as a society) no long spend energy to get energy, which has led to a number of health-related disorders, especially among our youth. From my perspective, drawing the link between brain and body has been fairly easy. The hard part is getting people to move again.
> Can exercise make you smarter even at an old age? What parts of the brain benefit the most?
Yes! The vast majority of work in this area has been focused on cognitive aging. That is, the study of physical activity, brain, and cognition has mainly been pursued in older adults. I am one of the first to turn the tables and show a similar relationship in children. Since Spirduso's work in the 1970s, physical activity and aerobic fitness has been found to relate to better cognitive health in older adults; so much so that some studies showed no differences between older active adults and younger adults. Only the older sedentary adults demonstrated cognitive decay.
What parts of the brain benefit most is a difficult question. People have their opinions. I will tell you that it is the prefrontal cortex (PFC). The PFC has been shown to be particularly susceptible to physical activity intervention, especially in older adults. The processes mediated by it, i.e., executive control processes, appear to benefit the most as well. Non-human animal researchers focus on the hippocampus, which also appears to be responsive to exercise. Other researchers show brain changes in different areas as well.
> Are there certain exercises that show more improvement in brain function than others? Is aerobic exercise best?
Aerobic exercise is the key. Work in my lab has shown that aerobic exercise leading to gains in aerobic fitness are most related to cognitive health and function, both in adults and children. We conducted one study that examined an acute bout of cardio and an acute bout of strength training. Only the cardio benefited cognition afterwards. The strength training was unrelated. Having said that, I am unwilling to make the statement that other forms of exercise, besides cardio, are not beneficial. Simply, much more work needs to be done, and we've only collected one study.
> Is there a minimum amount of time we need to exercise in order to have benefits for the brain?
No idea. This is the million dollar dose-response question. We simply don't know. I will say that a single bout of treadmill walking for 20 minutes improves cognitive health and function in kids and adults for a short period of time afterwards (about 45-60 min).
> Why has brain-derived neurotrophic factor (BDNF) become the most important factor with exercise and brain cognition?
It isn't! It is just the most publicized recently. There is a robust line of non-human animal research indicating that aerobic exercise upregulates BDNF, which is related to long term potentiation (neural underpinnings of learning) and neuronal survival. It is an exciting area, but it is not the only exciting area in the exercise-brain relationship.