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Neural basis of natural navigation: Representation of goals, 3-D spaces and 1-km distances in the bat hippocampal formation – the role of experience

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Bats in flight reveal how our brains navigate

Tracking neural activity in bats has revealed a great deal about how our brains navigate the space around us. This fundamental research could have implications for treating brain disorders, and even machine learning.

Fundamental Research

Neuroscientists have known for years that the hippocampal formation in the brain contains neurons that specifically relate to space, and is critically important for memory, and spatial memory in particular. “These neurons include place cells, which tell us where we are located in space,” explains NATURAL_BAT_NAV project coordinator Nachum Ulanovsky, professor of Brain Research at the Weizmann Institute of Science in Israel. “Grid cells, on the other hand, act like a ruler, enabling the animal to measure the space.” There are also head-direction cells, which act like a sort of compass, and border cells that identify the limits of a given space. Taken together, these neurons help us to navigate, and to localise ourselves in the context of our surroundings.

A naturalistic approach

Neuroscientists are only really beginning to fully understand how the navigational capacity of the hippocampal formation actually works. “In neuroscience, experiments are usually carried out in small, controlled environments,” says Ulanovsky. “Navigation in the natural world is different. So, we wanted to launch an open-ended project that takes a more naturalistic approach.” To achieve this, Ulanovsky replaced the usual mouse and lab maze experiments with a 200-metre long tunnel and a collection of bats. As bats fly in three dimensions, fly fast, and cover large areas, they are perfect for understanding the role of the brain’s hippocampus when navigating over long distances. Wireless neurophysiological devices to capture and store data were carefully attached to the bats. The animals were then tracked using a GPS-like system that offered exceptional positional accuracy.

Tracking brain power

Ulanovsky was able to show that bats flying towards navigational goals use neurons that represent both direction and distance. This vector, as it is called, was found for the first time in the hippocampus. “We were also able to show that there are specific neurons in the hippocampus that represent where other bats are,” adds Ulanovsky. “We called these social place cells. These could play an important role in how, for example, a footballer is able to find his teammates with a pass.” Tracking the bats also helped Ulanovsky to identify specific neurons that aid three-dimensional navigation, and how bats navigate over large spaces. Ulanovsky and his team found that bats use a sort of multiscale navigational code to represent their position in the long 200-metre tunnel. “What was interesting was that lab-born bats, which have never seen large spaces, used the same navigational code as wild bats,” notes Ulanovsky. “This suggests that this multiscale code is not dependent on experience, but is rather very robust and basic. Naturalistic behaviour projects like this can lead you to surprising results.” In terms of real-life applications, Ulanovsky suggests that it is too early to say what impact this fundamental research might have on the treatment of brain conditions. There is undoubtedly potential however, given that the hippocampal formation is where we form memories, and is the first region of the brain to exhibit signs of Alzheimer’s Disease. Another area of great potential is the discovery of how a bat uses a sort of multiscale code to navigate over large spaces. This finding could influence the development of navigational algorithms, including those based on machine learning.

Keywords

NATURAL_BAT_NAV, neurobiology, brain, bats, neurons, hippocampal, navigation, neuroscience

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