Put rats in an IMAX-like surround virtual world limited to vision only, and the neurons in their hippocampi* seem to fire completely randomly — and more than half of those neurons shut down — as if the neurons had no idea where the rat was, UCLA neurophysicists found in a recent experiment.
Put another group of rats in a real room (with sounds and odors) designed to look like the virtual room, and they were just fine.
“Since so many people are using virtual reality, it is important to understand why there are such big differences,” said Mayank Mehta, a UCLA professor of physics, neurology and neurobiology in the UCLA College and the study’s senior author.
When hippocampus neurons lose rhythm
When people walk or try to remember something, the activity in the hippocampus becomes very rhythmic and these complex, rhythmic patterns appear, Mehta said. Those rhythms facilitate the formation of memories and our ability to recall them. Mehta hypothesizes that in some people with learning and memory disorders, these rhythms are impaired.
The mechanisms by which the brain makes those cognitive maps remains a mystery, but neuroscientists have surmised that the hippocampus computes distances between the subject and surrounding landmarks, such as buildings and mountains. But in a real maze, other cues, such as smells and sounds, can also help the brain determine spaces and distances.
“Neurons involved in memory interact with other parts of the hippocampus like an orchestra,” Mehta said. “It’s not enough for every violinist and every trumpet player to play their music flawlessly. They also have to be perfectly synchronized.”
Mehta believes that by retuning and synchronizing these rhythms, doctors will be able to repair damaged memory, but said doing so remains a huge challenge.
The study was published in the journal Nature Neuroscience. The research was funded by the W.M. Keck Foundation and the National Institutes of Health.
* The hippocampus is a brain region (on both sides of the brain) involved in spatial learning and constructing and using mental maps.