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LA JOLLA, Calif. — The human brain has an interesting way of processing how close or far an object is from us in space. Look out of your car at night and chances are the Moon will look like it’s moving alongside you. A new neuroscience study has discovered why the memory area of our brain perceives close and far-away images and how these exaggerations can create more brain connections as we get older.

The hippocampus is a brain area involved in learning and memory. In the current study, the authors found that neurons associated with planning, memory, and spatial navigation turn space into a nonlinear hyperbolic geometric shape — think about an expanding hourglass growing bigger as you move away from it. Going back to the Moon example, young kids may have found the Moon to be following them or close enough to reach up for it.

Of course, the Moon isn’t actually moving anywhere, and its size is distorted because it is so far away. The results showed that the size of the image increases with more time spent in a place. The size our brains perceive is also directly linked to how much information can be processed by the brain — younger brains might be more likely to navigate and perceive space in a linear way. With new experiences, the hippocampus is able to refine its neural connections and process more information on the image.

The brain ‘expands’ with experience

Understanding how the neural networks in the brain process spatial navigation could help with studying neurocognitive disorders. Alzheimer’s disease, for instance, is one condition where the hippocampus is one of the first brain areas to be destroyed, affecting a person’s memory.

“Our study demonstrates that the brain does not always act in a linear manner. Instead, neural networks function along an expanding curve, which can be analyzed and understood using hyperbolic geometry and information theory,” says lead author Tatyana Sharpee, a professor at the Salk Institute and holder of the Edwin K. Hunter Chair, in a media release. “It is exciting to see that neural responses in this area of the brain formed a map that expanded with experience based on the amount of time devoted in a given place. The effect even held for miniscule deviations in time when animal ran more slowly or faster through the environment.”

The research team used advanced computational methods to understand how the brain works. One of these techniques involved using hyperbolic geometry to dissect biological signals. Previous work used hyperbolic geometry to look at how odor molecules and the perception of smell works.

Hyperbolic geometry appeared to work with understanding neural responses as well as being successful at mapping out sensory molecules and events. They collected their information through rats who spent time exploring a new environment. The more slowly and time the rat spent in an area, the more information it gained about the space around it. This, in turn, caused their neural map to expand and grow.

“The findings provide a novel perspective on how neural representations can be altered with experience,” says Huanqiu Zhang, a graduate student in Dr. Sharpee’s lab. “The geometric principles identified in our study can also guide future endeavors in understanding neural activity in various brain systems.”

The study is published in the journal Nature Neuroscience.

About Jocelyn Solis-Moreira

Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Health, and Live Science, among other publications. She holds a Master's of Science in Psychology with a concentration in behavioral neuroscience and a Bachelor's of Science in integrative neuroscience from Binghamton University. Jocelyn has reported on several medical and science topics ranging from coronavirus news to the latest findings in women's health.

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