How Animals Navigate Darkness

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TThe body may know where we are going before our eyes, constructing maps of the world that rely on a kind of internal GPS rather than landmarks or other visual cues. This process, known as path integration, allows the brain to track every step and turn you take, updating your position in time and space, even in the dark.

Certain neurons in the hippocampus, called place cells, play a central role in this process in the brain. They activate in specific locations, whether or not an animal can see its surroundings, relying on internal signals to decide which locations deserve special attention. Working together, neurons fire in patterns that follow the passage of time and distance during movement.

A team of scientists at Florida’s Max Planck Institute for Neuroscience recently discovered new details about how these internal maps work: Rather than using a single internal clock, the brain uses two sets of interacting excitatory and inhibitory neurons in the hippocampus. The researchers published their results in Natural communications.

Scientists have long known that the hippocampus helps animals navigate and that certain neurons fire at specific locations they visit. “However, in environments filled with sights, sounds and smells, it is difficult to tell whether these neurons are responding to these sensory signals or to the position of the animal itself,” Yingxue Wang, a neuroscientist at the Max Planck Neuroscience Institute in Florida and co-author of the paper, explained in a statement.

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To reduce noise, the researchers worked with mice, whose hippocampal circuits can be recorded and manipulated with high precision. They first trained the mice to run fixed distances along a virtual linear track to obtain a reward. The track had no obvious landmarks or visual cues, forcing the mice to rely on internal estimates of distance and time. As the mice ran the course, the researchers recorded the activity of hundreds of neurons. Next, they used light to disrupt certain inhibitory circuits and test how these disruptions shaped the animals’ perception of time and distance.

Once the recordings were collected, two distinct patterns emerged. A set of excitatory neurons called PyrUp was activated suddenly at the start of the movement, then gradually disappeared, each at its own pace. Taken together, these scaled activities appear to give the brain a measuring point, letting it know how far the animal has come on the journey. Another set, known as PyrDown excitatory neurons, showed the opposite pattern, calming down at the start of the movement and then gradually rising again. This activity helped mark the start of a new journey, preventing the brain from mixing one journey with the next.

From there, the team used light to silence two types of inhibitory neurons in the brain: SST neurons, which help stabilize the brain’s internal timing signals, and PV neurons, which act as a kind of reset button. When these neurons were silenced, the mice misjudged distance or time without changing their running speed. This finding reinforced the idea that PyrUp and PyrDown neurons encode internal measurements of time and space, rather than movement itself. Additional control experiments confirmed that the effects were not due to motor problems, visual deficits, or altered reward expectations.

If similar patterns were observed in humans, they could help explain why people with Alzheimer’s disease and other types of dementia often become disoriented, even in familiar places, and could point to new therapeutic targets to restore that lost sense of where we are.

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Main image: Rudmer Zwerver / Shutterstock

• Kristen French

  Published on December 17, 2025

  Kristen French is an associate editor at Nautilus. She has worked in science journalism since 2013, reporting and writing articles and news for publications such as Wired, Backchannel, The Verge, And New York Review. She holds a master’s degree in science journalism from Columbia University.