2024-02-08 17:47:21
Our sense of direction is essential to our ability to navigate the world around us. It acts as the brain’s internal compass to help us find our way, and just as importantly, to nudge us to change course when we’re going in the wrong direction.
However, despite a large body of research into how navigation in the brain works, scientists still lack a clear understanding of how this internal compass guides behavior directly.
Now, a study conducted in fruit flies and led by researchers at Harvard Medical School offers new insights into how two separate brain regions -; the compass seat and steering center -; communicate during navigation.
The findings are published on February 7 in Nature.
In the study, the researchers examined the brains of fruit flies that were knocked off their course while running in a certain direction. They discovered that three distinct groups of neurons enable communication between the compass and steering areas of the brain and work together to help the flight correct its course. In the process, the neurons translate signals from a fly’s internal compass into behavior to keep it moving in the right direction.
Until now, no one really knew how the sense of direction, which is an internal cognitive state, is related to the actions an animal does in the world.”
Rachel Wilson, senior author, Joseph B. Martin Professor of Basic Research in Neurobiology at the Blavatnik Institute at HMS
Despite their small size, fruit flies have complex brains and behaviors -; And thus the findings could provide a basis for future studies on how brain signals are translated into actions in more complex species, including humans.
Staying on track
Humans and other complex animals have an internal compass made of brain cells that use internal and external information to create a sense of direction. In fruit flies, scientists realized that these cells -; called head direction cells -; arranged in a circle, which makes them particularly easy to study.
Contrary to what their name suggests, fruit flies spend more time walking than flying. Previous studies have shown that while the flies are turning, these head-orientation cells actively monitor their turning movements, such as turning right or left.
In the new study, Wilson and his colleagues wanted to investigate how this compass is functionally connected to the steering area of the brain to understand how it guides navigation. To do this, they used an existing wiring diagram of every nerve connection in the fruit fly brain to build a computational model of how these areas might be linked. Using this model, they were able to identify and make predictions about the layer of neurons connecting the two regions.
To verify their predictions, the researchers analyzed the activity in the layer of neurons detected by the model as the flies moved around in a virtual reality environment. Often, flies ran straight in a random direction, presumably in an effort to escape their surroundings. As their virtual world rotated to move them off course, the flies were quickly repaired. Interestingly, these trajectory corrections were made by three separate sets of neurons: two sets of neurons prompted the fly to go right or left, and one issued a signal to turn completely.
“You can think of these three groups of neurons as three sentinels guarding a castle,” Wilson said, “with each one responsible for tracking in a different direction and guiding the correction needed to keep the fly moving toward its goal.”
The findings explain how fruit flies use their sense of direction to estimate where they are relative to a target and how they use this estimate to adjust their behavior.
“It’s a really concrete description of how a complicated cognitive process works and how it produces specific, guided behaviors in real time,” Wilson said.
The findings complement a second study, also published in Nature on February 7 and led by a separate team of researchers from Rockefeller University, which describes parts of the same neural circuit in fruit flies.
Together, the two studies provide an even more complete understanding of how the sense of direction translates into behavior in animals.
A strong starting point
Wilson said her team’s observations have implications beyond identifying connections between the brain’s compass and steering areas. The findings provide important clues about the format and location of navigational targets in the brain -; and may pave the way for understanding how other types of targets are stored.
“I think we’ve touched on one of the most mysterious aspects of brain function, which is how we covertly hold information and intentions in our minds and then act on them,” Wilson said, adding that even insects have this ability. . “In the future, we’re going to investigate how it works.”
Wilson is also interested in learning more about the three groups of neurons that the study identified -; And do other brain networks have analogous groups of neurons dedicated to fine and coarse adaptations.
“We have a feeling that this is actually the main principle of brain function and may explain many apparently redundant pathways in the brain,” Wilson explained.
Wilson added that because fruit flies have complex brains and behaviors, they are a good starting point for studying aspects of cognition that exist in higher-order species such as mice or humans.
“By understanding a system in one small brain, I think we’ve made important progress toward making clear hypotheses about how it might work in more complicated brains,” she said. “At this point, I don’t see a clear end to the similarities between the sexes.”
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