Non-invasive electrodes measure longer-latency brain signals in bats

A bat can emit 500,000 echolocation pulses each night. Each pulse integrates auditory feedback from the previous call in real time, allowing the bat to make informed decisions on the fly. Understanding how the bat’s auditory system processes sound has applications in biosonar comparisons, sonar drones, and language processing.

Fouhy et al. developed a method to take non-invasive measurements of auditory evoked potentials — which refer to the brain’s electrical activity in response to sounds — in Mexican free-tailed bats. Using a scaled-down electroencephalogram (EEG), they captured previously undescribed longer latency signals originating in the cortex.

The longer latency signals responded more to echolocation frequencies. They followed the same firing patterns as neurons in the cortex, reflecting the emphasis on echolocation frequencies in a bat’s auditory processing. Downward frequency sweeps used for echolocation elicited a greater response than upward frequency sweeps used in communication.

Yet in real-world scenarios, bats only gather useful information from echoes preceded by a pulse. The researchers presented bats with two complex stimuli: a pulse-echo pair and a five-pulse sequence. As expected, the pulse-echo pair elicited two rapid-response signals and a larger latent response than a single pulse. The five-pulse sequence caused only two rapid-response signals before a single latent response, implying that the cortex integrates information across time.

The team hopes to expand their work by equipping bats with wireless EEGs to study brain activity in bats while they echolocate, vocalize, and fly around.

“We have an opportunity to really increase what we know about how these higher brain regions are collecting and analyzing information over time,” said author Michael Smotherman, “That extends all the way to understanding how the human brain processes complicated sensory sequences.”

Source: Subcutaneous cortical auditory evoked potentials in echolocating bats,” by Victoria Fouhy, Sam Ellis, and Michael Smotherman, The Journal of the Acoustical Society of America (2025). The article can be accessed at https://doi.org/10.1121/10.0039659 .