HMN 2025: how the brain uses objects to find direction

We take our understanding of where we are for granted, until we lose it. When we get lost in nature or a new city, our eyes and brains kick into gear, seeking familiar objects that tell us where we are.

How our brains distinguish objects from background when finding direction, however, was largely a mystery. A new study provides valuable insight into this process, with possible implications for disorientation-causing conditions such as Alzheimer’s. The work is published in the journal Science.

The scientists, based at The Neuro (Montreal Neurological Institute-Hospital) of McGill University and the University Medical Center Göttingen, ran an experiment with mice using ultrasound imaging to measure and record brain activity. The mice were shown visual stimuli, either an object or a scrambled image showing no distinct object.

They found a small number of brain areas that fired especially when the mouse looked at objects. These areas were found in a brain region called the postsubiculum, which specializes in keeping track of where the animal is facing at any given time. Each direction activates a specific cell in the postsubiculum.

Objects in the mice‘s vision increased the firing of the cell responsible for the direction in which the mouse was looking. They also inhibited cells responsible for directions where the mouse was not looking. Together, this activity reinforced the mouse’s perception of where it was relative to the object.

While the postsubiculum was particularly sensitive to the presence of objects in the mouse’s vision, other brain regions were not, suggesting that object recognition is particularly important to the brain’s understanding of where it is and where the animal is looking.

This finding offers clues as to why humans with diseases such as dementia and Alzheimer’s often lose track of where they are. A recent study from Oxford University has shown that the accumulation of tau protein—a hallmark of Alzheimer’s—happens first in the brain regions responsible for spatial orientation.

“A very useful aspect of our study is it presents a very high-level understanding of two systems that interact together—the visual and spatial recognition systems,” says Stuart Trenholm, a researcher at The Neuro and the paper’s co-senior author.

“We have a decent understanding now of how they modulate each other. They are both very high-level brain functions and a lot of these neurodegenerative disorders lead to disconnections between these states, so that will be interesting to look into in the future.”

“Our results are incredibly surprising,” says Adrien Peyrache, a researcher at The Neuro and the paper’s co-senior author.

“Nobody would have predicted that object processing would occur in the navigation system and not in the visual cortex. For the first time, we have an inside-the-brain perspective of what an object is, and how we use an object to get a sense of the world around us.”

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