Echolocating bats use sound to navigate and make quick decisions about their calls and flight paths. However, their ability to “hear” these sounds can be disrupted by obstacles, background noise, or other bats making similar sounds. While we know a lot about how bats adjust to outside disturbances, we don’t know much about how they adapt when their hearing is interrupted internally. The question is: How do bats change their behavior when something in their brain affects how they process sound?
Researchers at Johns Hopkins University found that when bats can’t hear, they use a remarkable strategy to adapt. Bats quickly and effectively adjust when they can’t hear, showing for the first time that their brains are naturally prepared to switch to a “Plan B” when their hearing is impaired.
For their study, researchers trained bats to fly from a platform, down a corridor, and through a window to get a treat. Then, they had the same bats perform the task again, but this time with a key auditory pathway in the midbrain temporarily blocked.
This blockage doesn’t just mute sounds like plugging ears; it stops most auditory signals from reaching the deeper parts of the brain. The effect is temporary, caused by a drug, and lasts about 90 minutes.
When their hearing was blocked, the bats could navigate the course surprisingly well, even on the first attempt. Though they were less nimble and occasionally bumped into things, each bat quickly adapted and performed effectively.
To compensate, the bats adjusted their flight paths and vocalizations. They flew lower, stayed close to walls, and made more frequent and longer calls, which helped strengthen the echo signals they relied on for navigation.
Co-author Clarice A. Diebold, a former Johns Hopkins graduate student now a postdoctoral student at Washington University in St. Louis, said, “Echolocation acts like strobes, so they were taking more snapshots to help them get the missing information. We also found that they broadened the bandwidth on these calls. These adaptations are fascinating because we’d usually see them when bats compensate for external noise, but this is an internal processing deficit.”
Despite repeating the experiments, the bats’ compensation skills did not improve over time, indicating that their adaptive behaviors were not learned but rather innate and built into their brain circuitry. This finding shows how resilient the brain is to disruptions and external interference.
The researchers were surprised that the bats could still hear with this part of their brain disabled. They think the bats may have relied on an undiscovered auditory pathway or that other neurons, unaffected by the blockage, might help with hearing in ways they hadn’t previously understood.
Moss said, “You’d think an animal wouldn’t be able to hear at all. But it suggests that there might be multiple pathways for sound to travel to the auditory cortex.”
Researchers are further planning to determine how much the study applies to other animals and humans.
Moss said, “Can this work tell us something about human auditory processing and adaptive responses? Since no one has done this, we don’t know. The findings raise important questions that will be exciting to pursue in other research models.”
Journal Reference:
- Clarice A. Diebold, Jennifer Lawlor, et al. Rapid sensorimotor adaptation to auditory midbrain silencing in free-flying bats. Current Biology. DOI: 10.1016/j.cub.2024.10.045