How bats navigate a noisy world

In the dense forests of Central and South America, Seba’s short-tailed bats thrive, navigating through the trees and feeding primarily on pepper fruit while living in large communal groups.

These bats, nestled in the safety of hollow trunks and rocky caverns by day, emerge at night in search of food, guided by their unique ability to echolocate.

This bat navigation process involves emitting ultrasonic sounds that bounce off objects, creating an “image” of their surroundings based on the returning echoes.

But amidst the constant chatter and ambient noise of their colonies, how do these creatures manage to filter out and focus on the sounds critical for their survival?

Bat navigation: Echolocation and communication

A recent study led by Johannes Wetekam and Professor Manfred Kössl from Goethe University Frankfurt’s Neurobiology and Biosensors Working Group has shed light on this fascinating question.

Previously, it was believed that the brain’s higher regions were responsible for processing sounds.

However, research from 2021, conducted by the same team, revealed that this intricate processing begins in the brainstem — a part of the brain vital for controlling essential functions like breathing and heart rate.

Unlike prior studies that relied on artificial stimuli, the latest research focused on natural bat calls, including both communication and echolocation sounds.

“With our study, we wanted to find out what happens in deviation detection when, instead of meaningless stimuli, ones are presented to Seba’s short-tailed bat that actually occur in its auditory world,” explains Wetekam.

Taking a deep dive into bat brains

To conduct their experiments, the team inserted two ultra-thin electrodes under the bats’ scalps, recording brain waves while the animals were under general anesthesia to prevent any movement that could skew the results.

Remarkably, the bats’ brains continued to respond to sounds even in this state, providing a clear picture of how different calls are processed.

The findings revealed a distinct difference in how the brainstem handles echolocation and communication calls.

Echolocation sounds, which are crucial for navigating and avoiding obstacles, triggered stronger signals in the brainstem when they were less frequent, indicating a mechanism for deviance detection.

This suggests that bats are primed to respond more swiftly to these crucial navigational cues.

Communication sounds, on the other hand, did not show the same pattern, highlighting a tailored response system based on the type of sound and its importance for survival.

“Bats probably need to react faster during echolocation than when communicating with conspecifics,” presumes Manfred Kössl.

“The brainstem is the first station in the brain to receive the acoustic signals, which is why calculating the probability of echolocation calls might be necessary first of all there, and especially their echoes, so that the animal can dodge obstacles in good time.”

Surprising insights from bat brain waves

Moreover, the study uncovered that bats‘ brainstems do not just differentiate sounds based on frequency but can also detect rapid changes in frequency or volume, underscoring its sophisticated capacity for sound processing.

This challenges the traditional view of the brainstem as a mere relay station for auditory signals, positioning it as a critical component in the early stages of sound analysis.

“This is astonishing, as the brainstem is a rather young part of the brain that scientists did not previously think capable of any substantial involvement in signal processing,” says Wetekam.

“They saw its role more in receiving signals from the auditory nerve and transmitting them to high-level regions of the brain.”

These insights are not just a breakthrough in understanding bat echolocation but also hold potential implications for human medical research.

Conditions like ADHD and schizophrenia, characterized by difficulties in processing external stimuli, may benefit from these findings, suggesting that the lower regions of the brain, such as the brainstem, play a more significant role than previously acknowledged.

Additionally, by unraveling how the bat brainstem distinguishes between complex acoustic signals, researchers hope to gain deeper insights into the human brain’s ability to process and interpret complex speech patterns.

Bat navigation and brain research implications

In summary, this fascinating study on Seba’s short-tailed bats uncovers the sophisticated mechanisms of echolocation and communication processing in the bat brainstem, while paving the way for new understandings in human neurology.

By demonstrating that the brainstem plays a critical role in deciphering complex acoustic signals, this research challenges previous notions and highlights the potential for advancements in treating neurological disorders.

As we delve deeper into the echoes of bat communication and bat navigation, we uncover valuable insights that bridge the natural world with human health, showcasing the profound impact of animal studies on medical science and our understanding of the human brain.

The full study was published in the journal JNeurosci.

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