The motto is often to save as much knowledge as possible as quickly as possible. However, if you want to memorize information over the long term, you should not cram continuously, but take breaks from learning. Researchers have now shed light on the neural mechanisms behind this so-called spacing effect through studies on mice. In the case of longer intervals between the repetitions of learning, the animals therefore fall back on the same nerve cells instead of activating new ones. This suggests that retraining a nerve network that has already been used will root the memories more deeply in it, the researchers explain.
How does learning work and how is knowledge anchored in our brain? There are still many unanswered questions about the complex processes in our thinking organ. In principle, however, neuroscientists assume that nerve cells are activated during learning, which enables them to make new connections with others. This then leads to the storage of the information, which can then be called up again by activating the same group of nerve cells. The fact that learning breaks play a role in this concept was described over a century ago in humans and has now also been proven in many animal species. But the neural background of this spacing effect has remained unclear. The scientists led by Annet Glas from the Max Planck Institute for Neurobiology in Martinsried have now dedicated themselves to this research topic.
They chose the mouse as a model animal. Because, as is well known, basic neuronal mechanisms and brain functions are mostly similar in us and the small rodents. As part of the study, the sciences first carried out learning experiments in labyrinth structures. The rodents had to memorize the position of a hidden piece of chocolate in the complex system of corridors. The mice were given the opportunity to explore the labyrinth several times in a row and find the reward. Sometimes there were no breaks between the learning explorations and in other cases there were interruptions of varying lengths.
When mice learn with or without a break
As the scientists report, the experiments initially confirmed the effectiveness of the spacing effect: “Mice that we trained with longer breaks between the learning phases could not memorize the position of the chocolate as quickly,” reports Glas. “But the next day the animals’ memory was better when they had taken breaks from studying.” The optimum length of the break was 60 minutes.
In order to gain insights into the neural differences between learning with and without breaks, the scientists recorded the nerve cell activity in the animals’ brains during the labyrinth tests. In addition, the so-called in vivo calcium imaging technique was used, which can show the nerve activities in the brain of living animals in detail. The researchers focused their study on the prefrontal cortex, as this region of the brain is known to play a role in learning processes and other cognitive functions.
As they report, the test results of the nerve activity during learning with and without breaks show the opposite of what they had expected: “If three learning phases follow one another, it is actually obvious that the same nerve cells are activated,” explains senior author Pieter Goltstein from the Max Planck Institute for Neurobiology. “After all, it’s the same experiment with the same information. After a long break, on the other hand, one could rather imagine that the brain interprets the subsequent learning phase as a new event and processes it with other nerve cells, ”says Goltstein.
More deeply rooted memories
But when the researchers compared the nerve cell activities in the different learning phases, they found exactly the opposite: During the short breaks, the activation pattern in the brain fluctuated more than it did during the long breaks. In other words: In the learning phases that followed one another in rapid succession, the mice usually activated different nerve cells. After longer breaks, on the other hand, the nerve cells from the first learning phase were also used again later.
As the scientists explain, this finding appears plausible against the background of the spacing effect: By using the same nerve cells, the brain can possibly strengthen the links between them in every learning phase. There is therefore no need to create a completely new “wiring”, according to the explanation. “We believe that this is the reason why memory benefits from long pauses,” says Goltstein.
Thus, after more than a century, the study now provides deeper insights into the neural processes on which the demonstrably useful advice for effective learning is based: If you learn with interruptions, you have something of your knowledge for much longer.
Source: Max Planck Institute for Neurobiology, specialist article: Current Biology, doi: 10.1016 / j.cub.2021.06.085