What Rats Can Tell Us About Memory

You’ve likely heard about the many benefits of sleep. But you probably haven’t heard the latest. Scientists are currently investigating how sleep helps us navigate the world around us. Past research has shown that memory plays a major role in helping us move through space. If you remember a location from a past experience, you will be able to navigate it more easily in the future. However, if the area is completely new to you, you will have more difficulty determining exactly where you are.

When you walk around your house and enter different rooms, you don’t think much about it. However, what’s taking place in the brain is critically important, constantly keeping track of where you are in any given space. This brain function that we all possess is called spatial navigation.

Sleep also plays an important role in navigation, which is why scientists are studying this critical connection. One form of study involves the classic rat-in-a-maze experiment where researchers track an animal’s ability and speed in navigating a maze. This particular version of the experiment is conducted in three steps. The first step is pre-run rest. Before the rats enter the maze, they take a nap to conserve energy and get ready to run. Sleep also prepares the animal’s memory for the maze. For the second step, the rats run the maze. As they weave through the narrow pathways, their brains absorb everything they see. The last step of the experiment is known as post-run sleep.

“This is arguably the most important part,” says Dr. Z. Sage Chen, associate professor of Neuroscience and Physiology at the New York University School of Medicine (NYUSOM).

According to Dr. Chen, the post-run sleep portion of the research is when the rats recall the maze memories once again. During this step, scientists closely monitor the animal’s brain signals while they sleep. When the rats run the maze repeatedly, each run becomes easier and faster. Throughout each step of the experiment, the animals have surgically implanted electrodes attached to individual neurons. This allows researchers to record the specific signals that run through the rats’ brains while running the maze. These electrodes are specifically placed in the cortex and sub-cortical areas, located in the outer layer and largest portion of the brain.

These signals gathered from the brain go into a data acquisition system, which helps collect and analyze the data from the different neurons that fire while the rat was navigating the maze.

“After that, [the data] is put into an amplifier, a machine that magnifies the brain waves, so scientists can study it,” Dr. Chen explains.

The key takeaway of this experiment is that when the rats were sleeping after they run the maze, the same group of neurons that fired during the previous runs fires once again.

The findings offer substantial evidence that sleep, at least in rats, helps solidify memory which then goes on the help them navigate more effectively in the future. And while rats and humans clearly differ in many ways, past studies have shown they have similar brain structures to humans, so what happens in their brains is likely similar to what happens in ours.

One of the primary reasons for studying animals’ brains is to understand human brains better. Research projects like this one open the door to solving significant problems like sleep disorders and memory decline linked to aging. As more and more evidence surfaces about the many benefits of sleep, the best way to remember something may be to take a nap.