Professor Nicola Lautenschlager
As one can understand, since the research field is so young, there are lots of hypotheses and theories, but this is probably the area where we still have the biggest limit in terms of knowledge. However, there are quite a few interesting studies, sometimes using animal models, which investigate the question, “What mechanisms, physiologically, for example, do occur, so that the brain benefits directly from physical activity?” More recently, quite excitingly, there are now also study with human participants, investigating the biological background, so to speak, of this correlation. The easiest way, I think, to look at that is to look at two different groups of impact. One would be direct impact on the brain, and the other one would be indirect impact.
So let me start with the latter one. Indirect impact would be anything which benefits, for example, your cardiovascular health, like your blood pressure, your heart, your endocrinological system, your metabolism and therefore the brain benefits, secondary to that. Compared to direct impact, which would be increasing specifically the blood flow to the brain, and therefore assisting the brain with its performance in thinking, or even more excitingly, changing biomarkers, enzymes, hormones, directly in the brain. For example, research has shown that the brain-derived neurotrophic factor or BDNF which we know is very important to help us to learn new things and remember things, can be triggered and activated with physical activity, and this has now also been shown in human trials. Then, obviously not to forget about psychological impact of physical activity. So we do know that most people who find the right type of physical activity do enjoy this greatly, especially older people. It gives them more confidence. Very often it’s a social activity where they meet other people, and therefore usually it has a very good impact on their mental health, and therefore that benefits the brain as well, for example, via reducing stress levels.
If we look at that a bit closer, what biological changes physical activity can achieve in the brain, there are more recently some quite exciting findings in relation to, for example, pathological changes in the brain in association with Alzheimer’s disease or vascular dementia. For example, a study in healthy participants who had to do an aerobic exercise program for a year, could show with modern MRI technology that the volumes of certain areas of the brain, like the hippocampus, were actually growing after the 12 month exercise. Now that was a very unexpected finding, because usually our understanding is that the brain is not growing once you are older, and the study wasn’t designed so that the authors could answer the question why that would happen. But the growth in volume in the hippocampal area in the participants in the intervention correlated with higher levels of their BDNF. So the hypothesis the authors had was actually that the physical activity helped increase connections between the neurons, like creating additional synapses, which help with communication and therefore improve the memory, and that would have lead to the increase of volume.
Now that finding was in comparison to the control group, who not only did not have a growth of the volume but they had a loss of volume, in the same duration, which is what you really would expect in an older person.
Other research has more closely looked at Alzheimer’s disease pathology and there are some early suggestions that physical activity might also be able to directly impact on the amount of amyloid, which is one of the typical deposits associated with Alzheimer’s disease, being present in the brain. So there has been research showing that regular physical activity programs can actually reduce the concentration of that pathological protein you measure in the brain. Why that is the case is not really clear. There are some theories that that might have to do with insulin, because insulin is connected with the deposition of amyloid and we do know, for example, that people with Type 2 Diabetes have a higher risk of Alzheimer's disease.