The brain’s ability to perceive space expands like the universeThank you for reading this post, don't forget to subscribe!
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 follows them or that they can reach out and touch it. It appears to be much nearer than is proportionate to its true distance. As we go about our daily lives, we tend to think of ourselves as navigating through space in a linear fashion.
But Salk scientists have found that time spent exploring the environment causes neural representations to grow in surprising ways.
The findings, published in Nature Neurology on Dec. 29, 2022 show that neurons in the hippocampus, which are essential for spatial navigation, memory and planning, represent space in a way that conforms to nonlinear hyperbolic geometry—a three-dimensional space that grows exponentially outward. (In other words, it’s shaped like the inside of an expanding hourglass.)
The researchers also found that the size of this space increased with time spent in a given location. And the size increases in a logarithmic manner, which corresponds to the maximum possible increase in information processed by the brain.
This discovery provides valuable methods for analyzing data for neurocognitive disorders involving learning and memory, such as Alzheimer’s disease.
“Our study shows that the brain does not always operate in a linear fashion. Instead, neural networks function along an expanding curve that can be analyzed and understood using hyperbolic geometry and information theory,” said Salk Professor Tatiana Sharpy, the Edwin K. Hunter Endowed Chair, who led the study.
“It’s exciting to see that the neural responses in this area of the brain form a map that expands with experience based on the amount of time devoted to a location. The effect persisted even for minor 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. They have recently pioneered the use of hyperbolic geometry to better understand biological signals such as odorant molecules as well as odor perception.
In the current study, the scientists found that hyperbolic geometry also guides neural responses. Hyperbolic maps of sensory molecules and events are perceived with hyperbolic neural maps.
Spatial representations dynamically expand depending on the time the rat spends exploring each environment. And when the rat moves more slowly through an environment, it receives more information about the space, which causes the neural representations to grow even more.
“The findings provide a new perspective on how neural representations can be changed with experience,” said Huanqiu Zhang, a graduate student in Sharpee’s lab.
“The geometric principles identified in our study may also guide future efforts to understand neural activity in different brain systems.”
“You would think that hyperbolic geometry only applies on a cosmic scale, but that’s not true,” says Sharpy.
“Our brains work much slower than the speed of light, which may be why hyperbolic effects are seen in tangible spaces instead of astronomical ones. Next, we would 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.
About this spatial perception research news
Original Research: Free access.
“Hippocampal spatial representations exhibit a hyperbolic geometry that expands with experience” by Huanqiu Zhang et al. Nature Neurology
Hippocampal spatial representations exhibit a hyperbolic geometry that expands with experience
Everyday experience shows 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 the rat hippocampus that mediate spatial perception represent space according to a nonlinear hyperbolic geometry. This geometry uses an exponential scale and gives more position information than a linear scale.
We found that the size of the representation corresponded to the optimal predictions for the number of CA1 neurons. Representations also dynamically expand in proportion to the logarithm of the time the animal spends exploring the environment, consistent with the maximum mutual information that can be obtained. Dynamic changes track even small variations due to changes in the animal’s movement speed.
These results demonstrate how neural circuits achieve efficient representations using dynamic hyperbolic geometry.
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