Exercise Gives You More Brain Cells, But Do These Push Old Memories Out Of Your Brain?

This guy has exercised so much, he can't remember how to use a handrail. baranq/Shutterstock

In a groundbreaking study back in 2014, researchers discovered that when mice exercise, it causes new neurons to be born in a region of the brain called the hippocampus, and this pushes old knowledge out of their brains, making them forget things they had learned before exercising. This obviously came as quite a surprise to scientists, who began to worry that humans may also experience similar memory losses when exercising. Fortunately, however, a new study has revealed that this does not occur in rats, suggesting that it may be a species-specific quirk that only affects some animals.

The hippocampus plays a central role in learning and the formation of memories, and is one of the very few parts of the brain where new neurons are created after we are born. Previous research has shown that people who are physically fit tend to have larger hippocampi than those who do not, suggesting that exercise may stimulate this process, known as neurogenesis.

The discovery that mice who exercised developed more new hippocampal neurons than those who did not exercise therefore came as little surprise to scientists, yet they were astounded to find that when these neurons formed connections with other brain cells, they tended to overwrite existing connections, leading to memory loss.


Exercise has been shown to stimulate neurogenesis in the hippocampus. dreamerb/Shutterstock

However, writing in the Journal of Neuroscience, the authors of this latest study explain that rats are actually more intelligent than mice, and that their brains have more in common with those of humans, which is why they chose to investigate whether or not this same effect occurred in rats.

After training these rats to memorize their way around a maze, the researchers then placed the animals into two groups, one of which was given regular access to a running wheel while the other was forced to remain sedentary for four weeks. At the end of this period, the study authors measured the number of new neurons in the rats’ brains, discovering that those that ran every day had between 1.5 and 2.1 times more new hippocampal neurons than the sedentary rats. This was directly dependent upon the distance that these rats ran over the course of the four weeks, with those that ran the furthest experiencing the highest levels of neurogenesis.

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