Bat Brainstem Plays Key Role in Auditory Signal Processing

Results deemed “astonishing, as the brainstem is a rather primitive part of the brain that scientists did not previously think capable of any substantial involvement in signal processing.”

Seba’s short-tailed bat (Carollia perspicillata) filters out important signals from ambient sound and distinguishes between echolocation and communication calls. (Credit: Julio Hechavarría, Goethe University Frankfurt).

Seba’s short-tailed bat (Carollia perspicillata) lives in the subtropical and tropical forests of Central and South America, where it mostly feeds on pepper fruit. The animals spend their days in groups of 10 to 100 individuals in hollow trunks and rocky caverns, and at night they go foraging together. They communicate using sounds that create distinct ambient noise in the colony – like the babble of voices at a lively party. At the same time, the bats also use vocalizations to navigate their surroundings: a phenomenon known as echolocation, for which they emit ultrasonic sounds that reflect off solid surfaces. The animals then assemble these echoes into an “image” of their surroundings. But how does Seba’s short-tailed bat manage to filter out important sounds from constant ambient noise? A common explanation is that the brain constantly predicts the next signal and reacts more strongly to an unexpected signal than to an expected one. This is referred to as deviance detection, and neuroscientists led by Johannes Wetekam and Professor Manfred Kössl from the Neurobiology and Biosensors Working Group at the Institute of Cell Biology and Neuroscience at Goethe University Frankfurt are exploring its mechanisms. Together with colleagues, they were already able to show in 2021 that signal processing does not begin in high-level regions of the brain but already in the brainstem, which is responsible for controlling vital functions such as breathing and heart rate. However, these studies only used artificial stimuli that are not meaningful to the animals.

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