Neural pathways for navigation have been identified
summary: A new study has shed light on how fruit flies navigate by revealing the connection between their internal compass and directional brain regions. This study shows that three distinct neural populations translate directional signals into corrective actions, allowing fruit flies to effectively modify their trajectory.
These findings not only deepen our understanding of navigation in simpler organisms, but also lay the foundation for future research into the neural basis of behavior in more complex species, including humans.
By exploring the complexities of fruit fly brains, scientists have revealed basic principles of cognitive processing and behavior modification, and provided insight into how internal cognitive states such as a sense of direction are transformed into concrete actions.
- The study discovered that three groups of neurons help fruit flies correct their course by translating internal compass signals into navigational behavior.
- This research provides detailed insight into how directional sensing is functionally linked to orientation mechanisms in the brain, guiding navigation.
- The findings could help understand similar cognitive processes in higher species, revealing universal principles of brain function across different organisms.
Our sense of direction is essential to our ability to navigate the world around us. It serves as our brain’s internal compass to help us find our way and, just as importantly, to prompt us to change course when we’re headed in the wrong direction.
However, despite a large body of research on how navigation works in the brain, scientists still lack a clear understanding of how this internal compass directly guides behavior.
Now, a study in fruit flies led by researchers at Harvard Medical School offers new insights into how two different brain regions — the compass seat and the orientation center — communicate during navigation.
The results were published on February 7 nature.
In this study, researchers examined the brains of fruit flies that deviated from their path while running in a specific direction. They discovered that three distinct groups of neurons enable communication between the compass and guidance areas of the brain and work together to help the fly correct its course. In doing so, neurons translate signals from the fly’s internal compass into behavior to keep it moving in the right direction.
“Until now, no one really knew how a sense of direction, an internal cognitive state, relates to the actions an animal takes in the world,” said lead researcher Rachel Wilson, the Joseph P. Martin Professor of Basic Research at UCLA. Field of Neurobiology at the Blavatnik Institute at HMS.
Despite their small size, fruit flies have complex brains and behaviors, so the findings could provide a basis for future studies on how signals in the brain are transformed into actions in more complex species, including humans.
Stay on track
Humans and other complex animals have an internal compass made of brain cells that use internal and external information to generate a sense of direction. In fruit flies, scientists have discovered that these cells — called head direction cells — are arranged in a circle, making them particularly easy to study.
Contrary to what their name suggests, fruit flies spend more time walking than flying. Previous research has shown that when flies wander, these head direction cells actively track their rotational movements, such as turning right or left.
In the new study, Wilson and his colleagues wanted to explore how this compass is functionally linked to the orientation area of the brain to understand how navigation is directed.
To do this, they used an existing wiring diagram of every neural connection in the fruit fly brain to build a computational model of how these regions are connected. Using this model, they were able to identify and predict the layer of neurons connecting the two regions.
To validate their predictions, the researchers analyzed activity in the layer of neurons identified by the model as the flies walked around in a virtual reality environment. Often, the flies ran straight up in a random direction, most likely in an attempt to escape their environment.
When their virtual world was rotated to throw them off course, the flies quickly corrected course. Interestingly, these course corrections were carried out by three separate groups of neurons: two groups of neurons nudged the fly to turn left or right, and one signaled it to turn completely around.
“You can think of these three groups of neurons as three sentinels guarding the castle, each responsible for watching in a different direction and stimulating the correction needed to keep the fly moving toward its target,” Wilson said.
The results 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.
“This is a really concrete description of how a complex cognitive process works and how it produces specific, directed behaviors in real time,” Wilson said.
The results complement a second study, also published in nature on February 7, led by a separate team of researchers at Rockefeller University, describes parts of the same neural circuit in fruit flies.
Together, the two studies provide a more complete understanding of how sense of direction is translated into behavior in animals.
A solid starting point
Wilson said her team’s observations have implications beyond identifying connections between the brain’s compass and orientation areas. The findings provide important clues about the shape and location of navigational goals in the brain, and may pave the way for understanding how other types of goals are stored.
“I think we’ve touched on one of the most mysterious aspects of brain function, which is how we hold information and intentions latently in our minds and then act on them,” Wilson said, adding that even insects have this ability. . “In the future, we will investigate how this works.”
Wilson is also interested in learning more about the three groups of neurons identified by the study, and whether similar groups of neurons dedicated to fine and coarse adjustments exist in other brain networks.
“We have a hunch that this is actually a key principle of brain function and may explain a lot of seemingly redundant pathways in the brain,” Wilson explained.
Wilson added that because fruit flies have complex brains and behaviors, they represent a good starting point for studying aspects of cognition found in higher species such as mice or humans.
“By understanding a system in a small brain, I think we have made important progress toward forming clear hypotheses about how this works in more complex brains,” she said. “At this point, I don’t see a clear end to the similarities between species.”
Authorship, Funding and Disclosures
Additional authors on the paper include Elena Westend, Emily Kellogg, Paul Dawson, Jenny Lu, Lydia Hamburg, Benjamin Midler, and Saul Druckmann.
The research was supported by the National Institutes of Health (U19NS104655).
About this neuroscience research news
author: Dennis Nealon
communication: Dennis Nealon – Harvard
picture: Image credited to Neuroscience News
Original search: Open access.
“Converting a head direction signal into a goal-directed pointing command” by Rachel Wilson et al. nature
Converting a head direction signal into a target-directed steering command
To navigate, we must constantly assess the direction we are headed in, and we must correct deviations from our goal. The direction is estimated by toroidal attractor networks in the head direction system. However, we do not fully understand how a sense of direction is used to guide action.
Fruit fly Connective network analyzes reveal three groups of cells (PFL3R, PFL3L, and PFL2) that connect the head direction system to the locomotor system. Here we use imaging, electrophysiology and on-the-go chemical stimulation to show how these combinations work. Each population receives a shifted version of the head direction vector, such that the three reference frames are shifted by approximately 120° relative to each other.
Each cell type then compares its own head direction vector with the common target vector; Specifically, it evaluates the correspondence of these vectors via a nonlinear transformation. The outputs of the three cell groups are then combined to create motor commands.
PFL3R cells are recruited when the fly is directed to the left of its target, and their activity drives a rightward turn; The opposite is true for PFL3L. Meanwhile, PFL2 cells increase homing speed and are recruited when the fly is pointing away from its target. PFL2 cells adaptively increase steering force as directional error increases, effectively managing the trade-off between speed and accuracy.
Together, our results show how the brain’s space map can be combined with an internal target to generate action commands, via a shift from geocentric to body-centric coordinates.