STUDY ANALYSIS: Exercise Rewires the Brain

A victory for exercise advocates? Think again: this discovery will be used to create more drugs, not fit people

According to researchers from Canada and Toronto, exercise rewires the brains of mice and helps them to forget traumatic or drug-associated memories. Of course, it’s “only” a mouse study, but it clearly demonstrates two powerful related facts: I) that mind and body are not separate and II) that exercise is a powerful form of medicine indeed.

Unfortunately, in our present age, we need to be reminded by scientific studies of these facts, which were truisms in the ancient world.

Another unfortunate fact: such discoveries will not be used to get people exercising more.

But before we get on to that, let’s see what the researchers did.

The researchers have been looking at new ways to treat post-traumatic stress disorder, with a particular focus on whether stimulating neurogenesis—that is, the formation of new neurons in the brain—might be one fruitful approach. Exercise is already known to stimulate processes of neurogenesis, although the exact effects are still far from well understood.

As one of the study authors explains,

Neurogenesis is important for forming new memories but also for forgetting memories. We think this happens because when new neurons integrate into neural circuits, new connections are forged and older connections are lost, disrupting the ability to recall memories. We wanted to see if this process could help mice forget stronger, traumatic memories too.

The researchers gave mice strong shocks in different settings. First, they were shocked after leaving a well lit white box and entering a dark box scented with ethanol. They were then given a second shock in another environment. This was enough to elicit PTSD-like symptoms in the mice. Over a month later, they remained fearful of entering the original dark box. This fear extended to other dark boxes, showing a general sense of fear. The mice also explored less in other environments, avoiding open spaces—a clear sign of anxiety in rodents.

The mice were then put in two groups. One group had access to an exercise wheel for four weeks and the other didn’t. The ones with access to the exercise wheel had increased numbers of neurons in their hippocampus, a region associated with the formation of memories linked to specific places and contexts. They also displayed less severe PTSD-like behaviours than the mice that had not been able to exercise.

A further experiment showed that if the mice were allowed to exercise in the between the first and the second strong shocks, the development of PTSD-like symptoms was far less severe.

The researchers then completed more experiments to determine whether the growth of neurons in the hippocampus was responsible for the effects observed. A press release explains exactly what they did.

Firstly, the researchers used a technique called optogenetics, where they added light-sensitive proteins to newly-formed neurons in the dentate gyrus, allowing the neurons to be activated by light. When they shone blue light on these cells, the new neurons matured faster. After 14 days, the neurons had grown longer, had more branches, and integrated more quickly into the neural circuits of the hippocampus.

In the second approach, the research team used genetic engineering to remove a protein in the newly-formed neurons that slows down neuron growth. This also resulted in the neurons growing faster and increased incorporation into neural circuits.

Both these genetic approaches reduced PTSD-like symptoms in mice after double-shocking and shortened the time taken for the mice to forget the fear memory. However, the researchers found that the effect was weaker than they saw with exercise, and did not reduce the level of the mice's anxiety.

It looks like the beneficial effects of exercise on the behaviour of the mice goes well beyond simply the architecture of the hippocampus.

Finally, the researchers set up an addiction experiment to see if the beneficial effects of exercise would work for other conditions. Mice were given a choice between a saline solution in one room and cocaine in another, so that they would build up an addiction associated with the room containing the cocaine. The researchers showed that exercise and genetic engineering of the hippocampus made mice forget their addiction, including the fact that the second room contained cocaine.

The conclusion, then: exercise really does rewire the brain, strengthening it and making it—and the whole organism—more resistant to external harms. Pretty cool, right?

But don’t think that this means the researchers are going to be advocating exercise as a treatment for PTSD and addiction.