Mastodon Scientific Frontline: How bat brains listen out for incoming signals during echolocation

Sunday, August 7, 2022

How bat brains listen out for incoming signals during echolocation

Bats "see" with the ears. Scientists at Goethe University have found out how the auditory cortex is prepared for the incoming acoustic signals.
Credit: Hechavarria

When bats emit sounds for echolocation, a feedback loop modulates the sensitivity of the auditory cortex for incoming acoustic signals. Neuroscientists from the Goethe University Frankfurt found out. In a study published in the journal "Nature Communications", they show that the flow of information in the neuronal circuit involved reversed as the sound was generated. This feedback prepares the auditory cortex for the expected “echoes” of the sounds sent out. The researchers see their results as a sign that the importance of feedback loops in the brain is currently still underestimated.

Bats are famous for their ultrasound navigation: they orientate themselves through their extremely sensitive hearing by emitting ultrasound sounds and getting a picture of their environment based on the sound thrown back. For example, the eyelid nose bat (Carollia perspicillata) the fruits she prefers as food through this echolocation system. At the same time, the bats also use their voice to communicate with their peers, for which they choose a somewhat lower frequency range.

Neuroscientist Julio C. Hechavarria from the Institute for Cell Biology and Neuroscience at Goethe University, together with his team, examines which brain activities in the case of the eyewear nose go hand in hand with the vocalizations. In their latest study, the Frankfurters examined how the front lobes - a region in the front brain that is associated with the planning of actions in humans - and the auditory cortex, in which acoustic signals are processed, work together in the echolocation. For this purpose, the researchers used tiny electrodes on the bats, which recorded the activity of the nerve cells in the frontal lobe and in the auditory cortex.

In bats that emitted location sounds, the researchers were able to identify a feedback loop in the network of frontal lobes and auditory bark, which was previously completely unknown. Usually the information flows from the front flap, in which the sound generation is planned, to the hearing cortex, in order to prepare it for an acoustic signal to be expected soon. After the output of a location sound, however, the flow of information from the front flap to the hearing cortex decreased until it completely reversed: the information now flowed from the auditory cortex back to the front flap. Presumably, according to Hechavarria, this feedback loop prepares the auditory cortex even better for the reception of the sound reflections following the location sounds.

The neurobiologists simulated signals from the auditory cortex by electrical stimulation of the frontal lobe. The activity generated in the front flap actually led to the hearing cortex reacting more strongly to sound reflections. "This shows that the feedback loop we found is functional," summarizes Hechavarria. To illustrate the importance of the results, the neurobiologist uses the image of a motorway: “So far, it has been believed that the flow of information on this information superhighway is primarily in one direction and feedback loops are the exception. Our data show that this view is probably incorrect and feedback loops in the brain are much more important than previously thought."

It was surprising that no pronounced reversal of the flow of information could be observed in communication sounds. "It may be because the bats were kept alone in an isolation chamber and therefore did not expect an answer to their calls," Hechavarria suspects, continuing: "What makes our study so interesting, among other things, is that it opens new paths to to investigate the social interactions of bats. At this point we want to continue working in the future."

Source/Credit: Goethe University

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