Nav: Home

New clues emerge about how fruit flies navigate their world

May 22, 2017

Nestled deep inside a fruit fly's brain, specialized nerve cells knit themselves into a tiny compass. New results from neuroscientists at the Janelia Research Campus illuminate the architecture of this circuit and the neural forces that collectively move the compass needle.

In addition to revealing details about how fruit flies navigate, the results offer insight into a more grand and mysterious process: how brains create and maintain internal pictures of the outside world. That possibility is "the most exciting thing for us," says Vivek Jayaraman, a Janelia group leader. "It's a window into something that borders on cognition."

A brain structure shaped like a doughnut acts as the internal compass of the fruit fly, Drosophila melanogaster. Some of the nerve cells that form this structure, called the ellipsoid body, play the part of the compass needle. If a fly changes direction, for example, a patch of nerve cell activity changes direction too moving from cell to neighboring cell around the doughnut as a fly turns, Jayaraman and Johannes Seelig reported in Nature in 2015. Seelig, a former postdoctoral researcher at Janelia, is now a group leader at the Center of Advanced European Studies and Research in Bonn, Germany.

Now, Jayaraman and colleagues have gone a step further to show how the fly's brain creates such a precise neural needle.

A group of ellipsoid body nerve cells called E-PG neurons set up the compass needle, by effectively activating neighboring neurons and suppressing more far-flung nerve cells, Jayaraman and colleagues Sung Soo Kim, Hervé Rouault and Shaul Druckmann, all Janelia scientists, reported May 4 in Science. Those dynamics -- nearby activation and far-flung repression -- help maintain a single, stable heading direction on the compass.

But E-PG neurons don't act alone to move the compass needle, another collaboration between Jayaraman and Janelia Group Leader Shaul Druckmannshows. Like fingertips delicately resting on a ouija board, another group of nerve cells called P-EN neurons shift the needle, the researchers report May 22 in eLife.

P-EN neurons form a handlebar-shaped structure that sits above the ellipsoid body, where they are able to send signals to E-PG neurons and receive messages back. Perched atop the circular compass, these handlebar neurons are perfectly positioned to both steer the compass needle and respond to its movements. That spatial arrangement, described by Janelia neuroanatomist Tanya Wolff, tipped the researchers off to how the system might work. That's "one of the most beautiful things about this particular circuit," Druckmann says. "Having this intuition from the structure of how it may work is a huge boost."

The researchers studied flies genetically engineered so that certain neurons glowed when active. Daniel Turner-Evans, a Janelia research scientist, then used a sophisticated microscope to watch this neural activity in flies as they walked on a ball. Turner-Evans watched neurons glow, indicating activity in the E-PG compass neurons. But he also saw what appeared to be the P-EN neurons shifting that neural activity around as the flies turned. "You could see the interplay, the push-pull of the system," he says.

When P-EN neurons in the handlebar detect that a fly has turned, they send signals to E-PG neurons in the compass to nudge the needle slightly in the direction of the turn. "Essentially you have a set of puppet strings by which you can pull the activity one way or another," Jayaraman says. But it's not a one-way street. Information about the fly's current position then moves back to the handlebar P-EN neurons, keeping both sets of neurons informed about the fly's position.

Other experiments conducted by Janelia postdoctoral associate Stephanie Wegener showed that some individual P-EN neurons respond when the fly turns right and others respond when the fly turns left. Still, some undiscovered factors are likely shoring up the fly's navigational abilities, the researchers suspect. "We are by no means trying to say we understand how everything works," Wegener says. "We understand one part of the puzzle pretty well, but it's a rather small part of a big puzzle."

More clues come from neuroscientist Gaby Maimon's group at Rockefeller University in New York City. In a paper published online May 22 in Nature, he and colleagues describe the navigational roles played by distinct groups of P-EN neurons.

Jayaraman and his colleagues' progress came quickly thanks to the unique collaborative environment at Janelia, he says. "You can actually have theorists in the same room while the experiment is going on, talking incessantly to experimenters," he says. "That's a wonderfully Janelian thing, that ease of interaction and focus on collaboration." Rouault and Druckmann's theoretical understanding of how the system could work was tested with experiments, which offered results that researchers used to refine the theories.

Taking both an experimental and a theoretical approach should help the researchers as they dive in to deeper questions about the fly's navigation system. "We'd love to know the big picture," Jayaraman says. "How does this compass get used?"

In humans, a sense of direction is just one of many factors that go into making navigational decisions. A person might usually walk straight to reach the subway station, but on a hot day might instead make a detour to the market for a drink. Similar sorts of factors may influence decisions in the brain of a fruit fly. "We imagine this compass being used some of the time for some of the things the fly does," Jayaraman says.

He and his colleagues are working on ways to study those more complex decisions in fruit flies. Figuring out how the fruit fly creates and uses models of its environment may provide important clues about how we humans know where we are and where to go next

Howard Hughes Medical Institute

Related Nerve Cells Articles:

How hearing loss can change the way nerve cells are wired
Even short-term blockages in hearing can lead to remarkable changes in the auditory system, altering the behavior and structure of nerve cells that relay information from the ear to the brain, according to a new University at Buffalo study.
Lab-grown nerve cells make heart cells throb
Researchers at Johns Hopkins report that a type of lab-grown human nerve cells can partner with heart muscle cells to stimulate contractions.
Nerve-insulating cells more diverse than previously thought
Oligodendrocytes, a type of brain cell that plays a crucial role in diseases such as multiple sclerosis, are more diverse than have previously been thought, according to a new study by researchers at Karolinska Institutet in Sweden.
Aggregated protein in nerve cells can cause ALS
Persons with the serious disorder ALS, can have a genetic mutation that causes the protein SOD1 to aggregate in motor neurons in the brain and spinal cord.
Aggression causes new nerve cells to be generated in the brain
A group of neurobiologists from Russia and the USA, including Dmitry Smagin, Tatyana Michurina, and Grigori Enikolopov from Moscow Institute of Physics and Technology, have proven experimentally that aggression has an influence on the production of new nerve cells in the brain.
Researchers grow retinal nerve cells in the lab
Johns Hopkins researchers have developed a method to efficiently turn human stem cells into retinal ganglion cells, the type of nerve cells located within the retina that transmit visual signals from the eye to the brain.
Nerve cells warn brain of damage to the inner ear
Some nerve cells in the inner ear can signal tissue damage in a way similar to pain-sensing nerve cells in the body, according to new research from Johns Hopkins.
It takes a lot of nerve: Scientists make cells to aid peripheral nerve repair
Peripheral nerve injuries, such as those resulting from neuropathies, physical trauma or surgery, are common and can cause partial or complete loss of nerve function and a reduced quality of life.
Nerve cells use each other as maps
When nerve cells form in an embryo they have to be guided to their final position by navigating a kind of molecular and cellular 'map' in order to function properly.
What hundreds of biomolecules tell us about our nerve cells
Researchers at the Luxembourg Centre for Systems Biomedicine, of the University of Luxembourg, have, under Dr.

Related Nerve Cells Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Do animals grieve? Do they have language or consciousness? For a long time, scientists resisted the urge to look for human qualities in animals. This hour, TED speakers explore how that is changing. Guests include biological anthropologist Barbara King, dolphin researcher Denise Herzing, primatologist Frans de Waal, and ecologist Carl Safina.
Now Playing: Science for the People

#532 A Class Conversation
This week we take a look at the sociology of class. What factors create and impact class? How do we try and study it? How does class play out differently in different countries like the US and the UK? How does it impact the political system? We talk with Daniel Laurison, Assistant Professor of Sociology at Swarthmore College and coauthor of the book "The Class Ceiling: Why it Pays to be Privileged", about class and its impacts on people and our systems.