The reason why Nature Neuroscience feels like "the brain is about to explode."

Young children sometimes believe that the moon is following them, or that they can reach out and touch it
.
It looks much
closer than it really is.
When we move around in our daily lives, we tend to think of us as navigating
through space in a linear fashion.
But Salk's scientists found that taking the time to explore an environment caused neural representations to grow
in surprising ways.

The findings were published in Nature Neuroscience
.
Studies have shown that neurons in the hippocampus, which are critical 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 the space increased
with the amount of time spent in one place.
Its size increases logarithmically, matching
the maximum possible increase in information processed by the brain.

This finding provides a valuable way
to analyze data on neurocognitive disorders involved in learning and memory, such as Alzheimer's disease.

"Our study shows that the brain does not always move
in a linear manner.
Instead, neural networks run along an extended curve that can be analyzed and understood using hyperbolic geometry and information theory," said
Professor Tatyana Sharpee.
"What's exciting is that neural responses in this area of the brain form a map that expands
based on the time invested in a given place.
When animals run slower or faster in the environment, this effect applies to even small deviations
in time.
”

Sharpee's lab uses advanced computational methods to better understand how the brain works
.
They have recently pioneered the use of hyperbolic geometry to better understand biological signals like odor molecules, as well as the perception
of odor.

In the current study, the scientists found that hyperbolic geometry also directs neural responses
.
Hyperbolic graphs of sensory molecules and events are perceived using hyperbolic nerve
graphs.
The spatial representation expands dynamically as the rat explores each environment for a long time
.
And, when a rat moved more slowly in an environment, it gained more information about the space, which led to more growth in neural representation
.

Huanqiu Zhang, a graduate student in Sharpee's lab, said: "These findings provide a new perspective
on how neural representations change with experience.
The geometric principles identified in our study could also guide future understanding of neural activity
in various brain systems.
”

"You might think that hyperbolic geometry only works on cosmic scales, but that's not the case," Sharpee said
.
"Our brains work much slower than the speed of light, which may be why
the hyperbolic effect is observed in graspable space rather than astronomical space.
" Next, we wanted to learn more about how these dynamic hyperbolic representations
in the brain grow, interact, and communicate with each other.
”