Before GPS, people had to memorize landmarks and understand the relationship between speed, time and distance. For example, 10 minutes of fast walking would mean a distance of half a mile being covered.
According to a study done by Johns Hopkins researchers, rats have the ability to re-learn the learned relationship into a moment-by-moment reaction. It’s proof that the brain has a map it creates for itself.
Manu Madhav is one of the primary study authors, who said the hippocampus and adjacent areas help people to determine where they are. By firing patterns of neurons into the areas, it helps them to understand the map better.
There are two kinds of cues the brain gets:
External landmarks such as a red barn in the driveway or the silver mailbox in front of the house. The second cue is the result of one’s self-motion in the world similar to a step-counter. When calculating distance over time – based on step addition or speed, the brain can give you an idea of how far you went when there are no landmarks to use. This is known as path integration.
Is the estimate you get from a 10-minute walk always the same distance or an experience in the world?
Researchers wanted to find this out and looked at rats that ran laps on a circular track. They placed various objects to be landmarks in a dome and moved the shapes around. Like a computer game, the landmark speed was dependent on the speed of the animal, which led to an AR environment where rats saw them running faster or slower than they really were.
The team looked at the rats’ place cells, which fired when the animal visited a certain area that was familiar. When the rat thought it had done one lap and came back to the same location, the neuron would fire once more. Looking at the firing patterns, researchers could determine how quickly the rat believe it was running.
When the shapes were no longer being projected, the rats needed to rely on their self-motion cues to help them. What they found was that the neurons caused the rats to think they were still running slower or faster than they really were. According to researchers, the rats had a long-lasting change in how fast and far they moved with every step.
Madhav said it’s well-known that animals readjust their self-motion cues in development. As they get bigger, it affects the measurement of their steps. The lab test proves that recalibration takes place even into adulthood. It means the human body is constantly updating itself with physical movements in the world; updating the map in its head.
The study also found more evidence of how memories are created.
Johns Hopkins neuroscientist James Knierum said the hippocampus is involved in spatial mapping as well as creating conscious memories of everyday experiences. The first signs of Alzheimer’s disease are spatial disorientation and loss of memory, which cause the hippocampal neurons to die. The findings will help lead to even more research to understand the cause of Alzheimer’s and find possible cures for it and other neurodegenerative diseases.
Researchers say it can help understand the brain’s most complicated cognitive processing systems.
The research team is hoping to use the AR experiment to look at other areas of the brain and see how the activity aligned with the hippocampus to create an intelligible and useful internal world map.