A new study in the journal Current Biology shows that physical exercise after learning improves memory and memory traces, but only if the exercise is done in a specific time window and not immediately after learning.

“It shows that we can improve memory consolidation by doing sports after learning,” said study corresponding author Dr. Guillén Fernández, from the Radboud University Medical Center, the Netherlands.

In the study, Dr. Fernández and co-authors tested the effects of a single session of physical exercise after learning on memory consolidation and long-term memory.

“Seventy-two participants were randomly assigned to one of three age- and gender-matched groups; all learned 90 picture-location associations over a period of approximately 40 min,” the scientists said.

“In each group, half of the participants started at 9 a.m. and half at 12 p.m. to control for time-of-day effects.”

“Following a baseline cued recall test, participants in the immediate exercise (IE) group performed a 35-min interval training on an ergometer at an intensity of up to 80% of their maximum heart rate.”

“IE participants subsequently moved to a separate quiet environment for a three-hr delay period, where they watched nature documentaries, before returning to the exercise lab for a control session. This control session did not involve exercise but used the same context otherwise.”

“For the delayed exercise (DE) group, the protocol was identical but with the order of the exercise and control session reversed; for the no exercise (NE) group, both sessions before and after the delay period were control sessions.”

Participants returned to the lab 48 hr after initial encoding and performed a second recall test in the magnetic resonance (MR) scanner.

The scientists found that those who exercised four hours after their learning session retained the information better two days later than those who exercised either immediately or not at all.

The MR images also showed that exercise after a time delay was associated with more precise representations in the hippocampus, an area important to learning and memory, when an individual answered a question correctly.

“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,” the scientists said.

It’s not yet clear exactly how or why delayed exercise has this effect on memory.

However, earlier studies of lab animals suggest that naturally occurring chemical compounds in the body known as catecholamines, including dopamine and norepinephrine, can improve memory consolidation.

One way to boost catecholamines is through physical exercise.

“We will now use a similar experimental setup to study the timing and molecular underpinnings of exercise and its influence on learning and memory in more detail,” Dr. Fernández said.

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Eelco V. van Dongen et al. Physical Exercise Performed Four Hours after Learning Improves Memory Retention and Increases Hippocampal Pattern Similarity during Retrieval. Current Biology, published online June 16, 2016; doi: 10.1016/j.cub.2016.04.071