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The brain's ability to perceive space expands like the universe

Summary: Time spent in a new environment causes neural representations to grow in surprising ways.

Source: salk institute

Young children sometimes believe that the moon is following them or that they can reach out and touch it. It appears to be much closer than is proportionate to its true distance. As we go about our daily lives, we tend to think that we navigate space in a linear fashion.

But Salk scientists found that time spent exploring an environment causes neural representations to grow in surprising ways.

The findings, published in Nature Neuroscience on December 29, 2022, show that neurons in the hippocampus essential for spatial navigation, memory, and planning represent space in a way that conforms to nonlinear hyperbolic geometry—a three-dimensional expanse that grows exponentially. (In other words, it’s shaped like the inside of an expanding hourglass.)

The researchers also found that the size of that space grows with the time spent in a place. And the size is increasing in a logarithmic way that corresponds to the maximum possible increase in information being processed by the brain.

This discovery provides valuable methods for analyzing data on neurocognitive disorders involving learning and memory, such as Alzheimer’s disease.

“Our study demonstrates that the brain does not always act in a linear fashion. Instead, neural networks work along an expanding curve, which can be analyzed and understood using hyperbolic geometry and information theory,” says Salk Professor Tatyana Sharpee, Edwin K. Hunter Chair, who led the study.

“It is exciting to see that the neural responses in this area of ​​the brain formed a map that expanded with experience based on the amount of time spent in a given location. The effect still held for minute deviations in time when the animal ran slower or faster through the environment.”

Sharpee’s lab uses advanced computational approaches to better understand how the brain works. Recently, they pioneered the use of hyperbolic geometry to better understand biological signals such as smell molecules, as well as the perception of smell.

In the current study, the scientists found that hyperbolic geometry also drives neural responses. Hyperbolic maps of molecules and sensory events are perceived with hyperbolic neural maps.

This is a drawing of an hourglass
New experiences are absorbed into neural representations over time, symbolized here by a hyperboloid hourglass. Credit: Salk Institute

The spatial representations dynamically expanded in correlation with the amount of time the rat spent exploring each environment. And when a mouse moved more slowly through an environment, it gained more information about the space, which made the neural representations grow even larger.

“The findings provide a new perspective on how neural representations can be changed with experience,” says Huanqiu Zhang, a graduate student in Sharpee’s lab.

“The geometric principles identified in our study may also guide future efforts in understanding neural activity in various brain systems.”

“You would think that hyperbolic geometry only applies on a cosmic scale, but that’s not true,” says Sharpee.

“Our brains work much slower than the speed of light, which may be one reason why hyperbolic effects are observed in apprehensible rather than astronomical spaces. Next, we’d like to learn more about how these dynamic hyperbolic representations in the brain grow, interact, and communicate with each other.”

Other authors include P. Dylan Rich of Princeton University and Albert K. Lee of the Janelia Research Campus at the Howard Hughes Medical Institute.

See too

This shows the maze that the researchers used

About this news from spatial perception research

Author: Press office
Source: salk institute
Contact: Press Office – Salk Institute
Image: The image is credited to the Salk Institute

Original search: Free access.
“Spatial representations of the hippocampus exhibit a hyperbolic geometry that expands with experience” by Huanqiu Zhang et al. Nature Neuroscience


Spatial representations of the hippocampus display a hyperbolic geometry that expands with experience

Everyday experience suggests that we perceive distances close to us linearly. However, the actual geometry of spatial representation in the brain is unknown.

Here we report that neurons in the CA1 region of rat hippocampus that mediate spatial perception represent space according to a non-linear hyperbolic geometry. This geometry uses an exponential scale and produces more positional information than a linear scale.

We found that the size of the representation corresponds to optimal predictions for the number of CA1 neurons. The representations also dynamically expanded proportionally to the logarithm of the time the animal spent exploring the environment, in correspondence with the maximum mutual information that could be received. Dynamic changes accompanied even small variations due to changes in the animal’s running speed.

These results demonstrate how neural circuits achieve efficient representations using dynamic hyperbolic geometry.