A feedback loop sensitises the auditory cortex to acoustic reflections
Neuroscientists at Goethe University, Frankfurt have
discovered a feedback loop that modulates the receptivity of the auditory
cortex to incoming acoustic signals when bats emit echolocation calls. In a
study published in the journal “Nature Communications", the researchers show that
information transfer in the neural circuits involved switched direction in the
course of call production. It seems likely that this feedback prepares the
auditory cortex for the expected echoes of the emitted calls. The researchers
interpret their findings as indicating that the importance of feedback loops in
the brain is currently still underestimated.
FRANKFURT. Bats famously have an ultrasonic navigation system: they use their extremely sensitive hearing to orient themselves by emitting ultrasonic sounds and using the echoes that result to build up a picture of their environment. For example, Seba's short-tailed bat (Carollia perspicillata) finds the fruits that are its preferred food using this echolocation system. At the same time, bats also use their vocalisations to communicate with other bats. They use a somewhat lower range of frequencies for this purpose.
Neuroscientist Julio C. Hechavarría from the Institute of Cell Biology and Neuroscience at
Goethe University and his team are investigating the brain activities
associated with vocalisations in Seba's short-tailed bat. Their most recent
study investigates how the auditory cortex and the frontal lobe work together
in echolocation. The auditory cortex processes auditory information and the
frontal lobe is a region in the forebrain that is associated, in humans, with
tasks that include planning actions. To discover more about this, the
researchers inserted tiny electrodes into the bats' brains to record neural
activity in the frontal lobe and the auditory cortex.
The
researchers succeeded in identifying a feedback loop that had previously been
entirely unknown in the frontal lobe-auditory cortex network of bats emitting
echolocation calls. Information normally flows from the frontal lobe, where
call production is planned, to the auditory cortex to ready it to expect an
acoustic signal. But it was observed that the flow of information from the
frontal lobe to the auditory cortex diminished after the emission of an
echolocation pulse until the direction of information transfer switched
completely and information flowed from the auditory cortex back to the frontal
lobe. Hechavarría hypothesises that this feedback loop readies the auditory
cortex to better receive the sounds reflected back from the echolocation call.
The
neurobiologists simulated signals originating from the auditory cortex by
electrically stimulating the frontal lobe. The activity this generated in the
frontal lobe had the expected effect of prompting the auditory cortex to
respond more strongly to acoustic reflections. “This shows that the feedback
loop we found is functional", neurobiologist Hechavarría sums up. He takes up
the metaphor of a highway to illustrate the significance of these findings: “Up
to now, it was generally believed that the flow of data on this information
superhighway mainly runs in one direction and that feedback loops are
exceptions. Our data show that this view is most likely incorrect and that
feedback loops in the brain are probably considerably more significant than has
previously been hypothesised."
Surprisingly,
no pronounced reversal of information flow was observed for bat vocalisations
used for communication purposes. “This may be because the bats were alone in a
sound-proofed and electrically isolated chamber and therefore did not expect a
response to their calls", Hechavarría speculates before going on to note: “One
of the aspects that makes our study so interesting is that it opens up new ways
to study the social interactions of bats. We want to continue work in this area
in the future."
Publication:
Francisco García-Rosales, Luciana
López-Jury, Eugenia Gonzalez-Palomares, Johannes Wetekam, Yuranny
Cabral-Calderín, Ava Kiai, Manfred Kössl, Julio C. Hechavarría: Echolocation-related reversal of
information flow in a cortical vocalisation network. Nature Communications
13, 3642 (2022) https://doi.org/10.1038/s41467-022-31230-6
An image to download: https://www.uni-frankfurt.de/122772504
Caption:
Bats “see" with their ears. Researchers at
Goethe University have discovered how the auditory cortex is readied for
incoming acoustic signals. (Photo: Dr. Julio C. Hechavarría)
Further
information
Dr. Julio C. Hechavarría (Ph.D.)
Auditory Computations Group (Group Leader)
Institute for Cell Biology and Neuroscience
Tel. +49 (0)69 798-42050
Hechavarria@bio.uni-frankfurt.de
https://www.julio-hechavarria.com/