Bats’ Remarkable Backup Strategy for Silence Situations

They adjust quickly and effectively, indicating for the first time that bats’ brains are equipped with an innate capability to activate a backup plan when their hearing diminishes.

The research from Johns Hopkins University, recently published in Current Biology, prompts inquiries into whether other animals — and even humans — possess similar adaptive abilities.

“Bats exhibit an incredible flexibility in their behavior, allowing them to adapt at any moment,” explained senior author Cynthia F. Moss, a bat researcher at Johns Hopkins. “Other mammals and humans may also have these adaptive systems to help them navigate and make decisions, but what’s remarkable is how fast and almost automatic the bats’ responses are.”

All animals develop various strategies in response to a lack of sensory input. For instance, people in a noisy bar might lean in closer to hear better, while a dog may tilt its head toward an unheard noise.

The researchers aimed to investigate how echolocating bats, reliant on their hearing, would adjust when a vital part of their brain for auditory processing was disabled.

They trained bats to take off from a platform, navigate a corridor, and pass through a window for a treat. Then, the bats repeated the task with a significant auditory pathway in the midbrain temporarily blocked. This method of blocking the brain region doesn’t simply block hearing; it prevents most auditory signals from reaching deeper brain structures. This drug-induced approach is reversible and lasts approximately 90 minutes.

Despite the loss of hearing, the bats managed to navigate the course quite well, even on their first attempt. Although they were less nimble and bumped into a few things, all the bats adapted quickly and effectively.

“They faced challenges but found a way,” Moss remarked.

The bats altered their flight trajectories and vocalizations. They flew lower, aligned themselves with the walls, and increased both the number and duration of their calls, enhancing the echoes they rely on for navigation.

“Echolocation functions somewhat like flash photography, allowing them to take more ‘snapshots’ to gather the necessary information,” said co-author Clarice A. Diebold, a former graduate student at Johns Hopkins, now a postdoctoral researcher at Washington University in St. Louis. “Interestingly, we also observed that they expanded the bandwidth of these vocalizations. These adaptations are notable since such changes are typically seen when bats are dealing with external noise, instead of an internal processing challenge.”

Even after repeating the experiments, the bats didn’t show improvement in their compensatory skills over time. This indicates that the behaviors they used were not learned; rather, they were inherent, latent traits embedded in their brain circuitry.

“This underscores the brain’s incredible resilience to manipulation and external disruptions,” stated co-author Jennifer Lawlor, a postdoctoral fellow at Johns Hopkins.

The researchers were surprised to discover that the bats could still perceive sound, despite the temporary disablement of that part of their brain. They speculate that bats may have depended on an undetected auditory pathway, or that unaffected neurons could support hearing in unknown ways.

“One would assume that an animal wouldn’t hear anything at all,” Moss noted. “But this suggests there might be various pathways for sound to reach the auditory cortex.”

The next step for the team is to explore the extent to which these findings are relevant to other animals and humans.

“Can this research provide insights into auditory processing and adaptive behaviors in humans?” Moss posed. “Since similar studies haven’t been conducted, we don’t have those answers yet. The findings provoke essential questions that will be exciting to explore in future research.”

Co-authors include Kathryne Allen, Grace Capshaw, Megan G. Humphrey, Diego Cintron-De Leon, and Kishore V. Kuchibhotla from Johns Hopkins.