Neural circuits help flies stay on course

noNavigating the environment is a critical skill for many organisms. Scientists have wondered for years how the brain summarizes input from the environment, compares it with the animal’s desired destination, and guides the organism to successfully navigate it. But probing these questions in the complex mammalian brain has proven difficult.

In two studies, NatureResearchers from Harvard and Rockefeller universities have peered into the tiny brains of fruit flies to uncover the neural circuits that make those calculations happen. They explained how a neuron called PFL3 integrates information about the insect’s current location with information about where it wants to go. Meanwhile, the Harvard scientists have found that another group of brain cells, Anti-goal neuronsA research team from Rockefeller University has described a set of neurons that helps flies correct their course when they stray too far from their goal. The purpose of insects.^1,2 These studies combine experimental and modeling approaches to Drosophila melanogasternavigation and provide insight into underlying principles that may guide more complex navigation in the brain.

“These behaviors they’re seeing — goal-directed maneuvering — are common to all moving animals.” Daniel Turner Evans“It’s just amazing to see how these behaviors play out across different layers and neurons in the brain, and how we can create really nice conceptual and quantitative models that really match the anatomy and biology,” said UC Santa Cruz neuroscientist Robert F. Schneider, who was not involved in the study.

In insects, a highly conserved collection of brain structures, the central complex, is key in integrating various sensory inputs and directing movement during navigation. Several neurons in this complex Internal compass Some represent the direction of the fly relative to the landmarks, while others represent the direction of the insect’s Body Steering.^3,4 by Reconstructing neuronal connections Scientists have studied the brains of various insects. Different cell types.^5,6 For example, the compass neuron PFL3 neurons.⁷ Fly brains have two sets of PFL3 cells, with neurons in each hemisphere sending projection signals to a steering center on the opposite side. These previous findings suggested that PFL3 cells may enable insects to directly compare their heading with a target and adjust their trajectory to match the two.

Latest Nature In their paper, the researchers set out to experimentally test this idea and also to investigate this navigation circuitry in more detail. The teams recorded neural activity from tethered flies walking inside a floating sphere. “This basically acts as a treadmill: the fly can run, but because it’s a ball, the fly can also turn,” they explained. Elena Westende,graduate student Rachel Wilson“The researchers found that the flies were able to walk in a straight line for long periods of time, allowing the researchers to infer the direction the insects were heading each time they repositioned the visual cues,” said David Schneider, a researcher in the Harvard University lab and co-author of one of the studies. In both papers, the researchers placed a spherical treadmill in a virtual reality environment and presented the flies with a bright bar — a known stimulus that attracts insects. The flies walked in a straight line for long periods of time, allowing the researchers to infer the direction the insects were heading each time they repositioned the visual cues.

In both studies, the researchers found that PFL3 neurons were involved in redirecting a fly’s body when it strayed from its intended path: For example, when a fly went to the left of its goal, PFL3 cells on the right side of the brain fired to correct the fly’s course, while the opposite happened for PFL3 neurons on the left side.

Nearly all of the inputs that PFL3 cells receive are shared with another group of neurons called PFL2, so Westeinde and his colleagues investigated the role of these cells in fly navigation. They found that PFL2 neurons fire actively when the fly is facing away from its goal. When the team stimulated these cells, the insects increased their turning speed. “It’s as if they’re saying, ‘No, that’s really wrong! Just turn back and get closer,'” Westeinde explained.

At Rockefeller University, Gaby MaimonThe team decided to look upstream of PFL3 to find cells that code for information about goals. As a fly walked on a spherical treadmill, the researchers rotated the ball several degrees and watched how certain neurons fired. They found that the activity of a group of cells called FC2 did not change when the fly turned in a different direction. To confirm that these cells code for a representation of the insect’s goals, Peter Massells PiresA postdoctoral researcher in Maimon’s lab and his colleagues optogenetically stimulated FC2 neurons.[When] Peter stimulates these FC2 goal-transmitting neurons, [he] You can make the fly walk in different directions,” Maimon explained.

Although Maimon’s work showed that FC2 neurons read the goal location, Turner-Evans still wants to know how the insect’s brain sets its goal. Exploring this question is one of Maimon’s next steps. Turner-Evans also thinks that an important next step will be to explore how these steering signals are sent to complex motor networks that are then translated into movement.

Although the fly brain is much simpler than the human brain, extensive characterization by researchers over the years has made it a powerful system for understanding how the brain processes information. “In flies, we’re able to discover these fundamental principles that seem to be somewhat universal,” Turner-Evans says. “I wouldn’t be surprised if some of the conclusions we’ve drawn from these studies prove to be true by looking at how animals turn for navigation.” [in] “mammalian”