Subcutaneous cortical auditory evoked potentials in echolocating bats.

Abstract

Auditory brainstem responses offer a convenient non-invasive method for assessing auditory system physiology, but mainly reveal activation of early brainstem and midbrain processing stages. With minor adjustments, the method can also capture slower cortical auditory evoked potentials (CAEPs). CAEPs have not been previously described in bats but are often used in large animals and humans to study cortical signal processing. Here, we describe two late peaks in the bat (Tadarida brasiliensis) auditory evoked potential waveform that appear cortical in origin. The first deflection (P1) peaked at 23 ms and showed the same onset (∼10 ms) and duration (∼20 ms) as ensemble neuronal activity in the auditory cortex under matched conditions. A second, smaller wave (P2) peaked at 37 ms, correlating with evoked activity in a secondary auditory region known as the frontal auditory field. Both peaks varied in amplitude and timing depending on acoustic stimulus properties. Notably, P1 was reduced at presentation rates above 8 Hz, consistent with predicted effects of cortical forward suppression. These findings demonstrate that robust CAEPs can be non-invasively recorded in bats and carry information about stimulus features and underlying neural mechanisms.