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How navigational goals are represented in the bat brain

American Association for the Advancement of Science

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IMAGE: Photo of an Egyptian fruit bat. Sarel et al. report on a new functional class of hippocampal neurons in bats, which encode the direction and distance to spatial goals -... view more

Credit: Steve Gettle

In bats, researchers have identified a subpopulation of neurons that represent navigational goals, a new study reports. The results provide valuable insights into how bats fly from A to B. To date, much research has shed light on the neural representation of an animal's own location and orientation, yet how spatial goals are encoded in the brain remains unclear. To gain a better understanding, Ayelet Sarel and colleagues trained Egyptian fruit bats to fly in complex patterns and land at a specific site, defined as the goal, where the bats could eat and rest. While the bats completed this task, a wireless electrophysiology device recorded individual neural activity in their hippocampus. About 19% of neurons recorded were found to act as "tuners," which varied in activity based on the angled directionality of a bat's flight path toward its goal. The authors note, however, that during real-life navigation the goal could be invisible to the animal, meaning that goal-directed navigation requires memory. Thus they conducted a second experiment where they masked the goal with an opaque curtain that blocked vision, echolocation, and olfaction. A substantial fraction of cells (43 of 158, or 27%) exhibited significant directional tuning to the hidden goal, suggesting that these goal-directed neurons also capture memory. When the goal was shifted in position, a portion of goal-directed tuning neurons changed, suggesting that some neurons are goal-specific. In a final experiment, a subset of neurons responsible for calculating distance towards the goal was identified. Most of these goal-distance cells fired maximally at short path distances of between 0 and 2 meters as the bat approached the goal.

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