Neuroscientists had a problem. For decades, researchers had a theory about how an animal's brain keeps track of where it is relative to its surroundings without outside cues—like how we know where we are, even with our eyes closed. According to the theory, which was based on brain recordings from rodents, networks of neurons called ring attractor networks maintain an internal compass that keeps track of where you are in the world.
An accurate internal compass was thought to require a large network with many neurons, while a small network with few neurons would cause the compass's needle to drift, creating errors. Then researchers discovered an internal compass in the tiny fruit fly. "The fly's compass is very accurate, but it's built from a really small network, contrary to what previous theories assumed," says Janelia Group Leader Ann Hermundstad.
"So, there was clearly a gap in our understanding of brain compasses." Now, research led by Marcella Noorman, a postdoc in the Hermundstad Lab at HHMI's Janelia Research Campus, explains this conundrum. The new theory shows how it is possible to create a perfectly accurate internal compass with a very small network, like in fruit flies .
The findings are published in the journal Nature Neuroscience . The work changes the way neuroscientists think about how the brain carries out many tasks, from working memory to navigation to decision-making. "This really expands our knowledge of what small networks can do," Noorman says.
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