If you develop Alzheimer’s disease, you not only lose your sense of time, but you also lose your sense of place. Could time and place be two sides of the same coin?

Around 55 million people globally are currently living with dementia, such as Alzheimer’s disease, a number that is expected to triple by 2050. At the Institute of Basic Medical Sciences at the University of Oslo, researchers are working to get closer to understanding what happens in the brain, so that we can prevent or slow the development of such diseases.

“All memories are made up of different components. You don’t just remember what you had for dinner yesterday, but also the time and place”, says professor Koen Vervaeke. “We often think of time and space as separate categories, a distinction created by philosophers and physicists that is incredibly practical for organizing our lives. But our brain cells don't see it that way.”

These cells don't distinguish between a step forward in space or a second passing in time. Instead, they simply record a continuously changing stream of information from our senses, tracking events as they unfold. To the brain’s internal network, time and place are effectively two sides of the same coin, he explains.

“In Alzheimer's disease, it is therefore not surprising that both are affected; when the neural network is damaged, our sense of "where" and "when" begins to unravel together”.

The scent of silence: Watching the brain’s internal relay
Remembering where, when and how something happened is called episodic memory. In your brain, billions of nerve cells form large networks, passing signals like a relay race to process information from your senses, the sounds, smells, and sights of your life.

We already know that cells which link memories to time and space are found in the hippocampus. But Vervaeke and his research group had a theory that another area of the brain is also involved, namely the retrosplenial cortex. Located at the back of the cerebral cortex near the hippocampus, this area was previously only known for linking memories to place.

To test if this area also tracks time, the team designed a memory challenge for mice. The task required them to hold a specific odor in their "working memory" during a brief period. The article was recently published in Cell Reports.

“We presented the mice with a simple sequence: one odor, a five-second pause, and then a second odor. If the two odors were different, banana followed by mint, the mice licked a tube for a sugar water reward. If the scents were the same, they had to stay still,” explains Vervaeke.

At first, the mice were impatient and licked the tube constantly. But after a week of training, they mastered the task.
“They learned to use that five-second silence to hold the first memory in their minds, waiting to see if the next scent would match or change” explains Vervaeke.

The universal script: A unified theory of experience
To see what was happening inside the brain, the researchers used a microscope to monitor nerve cells in the retrosplenial cortex while the mice performed their task.
“Under the microscope, we saw two distinct groups of nerve cells spring to life,” says Vervaeke. “The first group acted like scent experts, active only when a specific odor, like banana or mint, was present. But the second group was even more fascinating: these cells were active in a precise sequence during the five-second silence.

Like a relay race, one cell would pass the signal to the next, 'holding' the memory of the first scent until the second one arrived.
“By working together, these cells did two jobs at once: they identified the smell and tracked exactly how much time had passed.”

The most striking discovery was that the retrosplenial cortex uses the same "neural script" for both space and time. “We found that the sequence of neuronal activity in the retrosplenial cortex looks almost identical whether a mouse is physically running through a room or simply holding a memory in its mind for five seconds,” says Vervaeke.

Redefining reality to cure dementia
This discovery brings us back to the tragic reality of Alzheimer’s disease, where those affected struggle to anchor themselves in both time and place. By showing that the brain uses the same "neural script" for both, our research explains why these two senses often fail together, says the professor.

This work also challenges how we perceive the world around us. While we use the concepts of time and space to organize our lives, this distinction is largely a human construct. In fact, some modern theories in physics are moving away from using time and space as the fundamental building blocks of the universe. It appears the brain’s internal wiring mirrors this deeper reality, he says.

“We still have an enormous amount to learn about how a healthy brain functions,” Vervaeke explains. “It is nearly impossible to repair a car if you don’t first understand how the engine works when it’s running smoothly. Similarly, we must understand the 'blueprints' of a healthy brain, how it builds and stores these episodic memories, before we can truly grasp what goes wrong in dementia. These findings bring us one step closer”.

Read more:
Area-specific encoding of temporal information in the neocortex
https://www.cell.com/cell-reports/fulltext/S2211-1247(25)00134-2