Most of the people we find lifting weights in the gym or running laps around the track are doing so to improve their physique. While there are people who exercise to improve their mood, it’s safe to say that few do so to improve their ability to retain memories or even ward off neurodegenerative diseases such as Alzheimer’s or Parkinson’s.

In a recent study, published in the Cell Press journal Current Biology, the Donders Institute at the Radboud University Medical Center in the Netherlands analyzed the impact physical activity has on the brain’s ability to consolidate memories. Their findings show that anyone looking to retain important information should exercise four hours after learning it to make sure it sticks.

"Our results suggest that appropriately timed physical exercise can improve long-term memory and highlight the potential of exercise as an intervention in educational and clinical settings," said the research team in a statement.

Lead researcher Guillén Fernández and his colleagues examined the impact of a single session of physical activity — 35 minutes of interval training on an exercise bike at an intensity of up to 80 percent of participants' maximum heart rates — on memory consolidation and long-term memory.

They recruited 72 healthy male participants and showed them 90 different pictures that were presented on six specific locations on the screen. Each was asked to remember which object they were shown and its location before being assigned to one of three groups: The first performed the exercise immediately, the second performed it four hours later, and the third did not exercise. The researchers conducted a similar test of memory 48 hours later while taking brain images using an MRI.

Participants who exercised four hours after the learning session had an easier time retaining the information two days later compared to the others. Images from the MRI revealed that exercising four hours later led to stronger and clearer memory traces in the hippocampus, an area of the brain essential to learning and memory, when they answered correctly. Memory traces, also known as engrams, refer to hypothetical changes in brain cells that are brought on by memorization.

Similar studies have shown that exercise increases neuroplasticity, the brain’s ability to change and make new connections. Researchers from the Department of Biomedicine at the University of Basel in Switzerland conducted a similar study using two groups of mice that were either given running wheels or left to be sedentary. Although both were able to distinguish between similar and distinct objects an hour and a half after completing the task, only active mice could still do so 24 hours later.

Upon further investigation, this research team found that mice with running wheels developed twice as many new brain cells compared to sedentary ones. This led to an increase in the number of new synaptic contacts between nerve cells, especially in the hippocampus. Other studies have shown that specific chemical messengers activated by exercise play a role in sharpening our memory. These naturally occurring neurotransmitters, called catecholamines, include epinephrine, dopamine, and norepinephrine and can improve our ability to consolidate memories.

“They are neurotransmitters that release in several locations in the brain during physical exercise,” Fernández told Medical Daily. Their release helps stabilize memory traces after they are initially encoded by the brain. “The next step will be determining exactly which neurotransmitter is doing the trick,” he added. “We will also focus on what type of workout works best, what people do in the four hours between learning and exercise, and if processes behind these neurotransmitters lead to any pharmacological developments.”

Aside from exercise, Fernández said there are other ways of activating catecholamines. They are also essential to the fight-or-flight response, our psychological reaction to an attack or threat. In the face of a harmful or traumatic event, our brains trigger the release of catecholamines, which determine how we react to that stress. This is part of why we have such a strong response to situations perceived as threatening.

Source: van Dongen E, Fernández, G, et al. Physical Exercise Performed Four Hours after Learning Improves Memory Retention and Increases Hippocampal Pattern Similarity during Retrieval. Current Biology . 2016.

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