What's memory? How does the brain process sensory information to create a new one? And why do patients with certain cognitive disorders lose the ability to "remember"? New research by Mayank Mehta, PhD, neurophysicist at UCLA, is bringing scientists closer to answering these questions.
Dr. Mayank, a professor at the David Geffen School of Medicine at UCLA in the department of Physics & Astronomy, has spent decades studying the hippocampus — the part of the brain responsible for both memory and finding one's way. His latest study on space-mapping neurons (essentially the brain's own personal GPS system) resolves a neurological mystery that has long puzzled scientists: Does the brain create spatial memories based on visual landmarks or by tracking distances traveled?
By observing rats' hippocampal activity, according to News Medical, Dr. Mayank's team discovered that visual landmarks actually play a key role in identifying location. The experiment also came to some surprising conclusions that could reshape how engineers approach virtual reality, and how neurobiologists approach the treatment of Alzheimer's, epilepsy, PTSD and other learning- and memory-related conditions.
The experiment
Dr. Mayank Mehta
Dr. Mayank's team created a sophisticated virtual reality environment that cost half a million dollars to develop and build. Gently harnessed rats ran on a treadmill-like device surrounded by large screens displaying the "virtual world." Then, researchers tested the same rats in a real-world environment that mirrored this virtual environment.
"The rats behaved in virtual space as if it was normal space," says Dr. Mayank. "They went to places in the virtual world where they got rewards and avoided places without rewards. They licked only those places where they expected food."
Previous studies have yielded the same result, suggesting rats perceive virtual reality as real. But Dr. Mayank's team discovered something new: Although the rats were fooled, their brains weren't.
When Dr. Mayank's team examined subjects' brain activity, they found that nearly 60 percent of the space-mapping neurons shut down in virtual reality.
The theory
"This is not easy to explain," says Dr. Mayank. "Our current theory, which we're testing, is that when you move around in the real world, your brain keeps careful track of not only what you see but also what you hear and smell, and how much your body moved. These things change consistently with each other. But when you move in virtual reality, the smells and textures do not change consistently with the vision, because the subjects don't actually go anywhere."
According to Dr. Mayank, neurons in the hippocampus put together information from all these different senses to create a perception of reality. "The senses are always in register in the real world. In virtual reality, everything is not in perfect register. We believe that's how our brains know it's not real, and because things are not in sync in virtual reality — even in the sophisticated one we built — 60 percent of the brain shuts down."
The implications
Dr. Mayank and his team are working to further understand how memories are made and how they could be better preserved.
"Spatial-memory formation is only one part of the story," he explains. "We also found links between running and increased brain rhythms, which play a crucial role in learning and memory." In a previous study, Dr. Mayank learned that a very complex dialogue takes place among the space-mapping neurons in different parts of the brain during sleep; this could play an important role in forming long-term memories as well. It should be possible to integrate these findings to determine how people can make memories last longer.
Because virtual reality could turn off 60 percent of the neurons, he suggests, they have a big head-start. Why? Because his team can turn neurons on and off naturally, without any drugs. They can effectively use these findings to control neural activity and rhythms to make "better memories."
By Taylor Mallory Holland
