Vertical stripes in the spectrogram: Effects of onset transients on sustained responses in inferior colliculus neurons

Rapid acoustic onsets are prominent in natural sounds like speech and rustling, cueing scene parsing, event detection, and attention. Octopus cells (OCs) in the cochlear nucleus are specialized for detecting these sharp onsets and relay precisely timed inhibitory signals to the inferior colliculus (IC) via the ventral nucleus of the lateral lemniscus.1 While this pathway is anatomically defined, how rapid onsets influence downstream auditory processing in the IC remains unclear.2 To address this, we presented brief clicks and assessed their impact on tone-evoked IC responses in awake, head-fixed mice. A PSTH-based linear model revealed sublinear integration, indicating suppression when clicks and tones coincided. This suppressive effect peaked at zero delay, consistent with fast, onset-driven inhibition. Additionally, varying the onset gate duration of tones by sub-millisecond steps modulated IC firing rates, highlighting the IC’s sensitivity to fine temporal features. These findings suggest that rapid onsets engage precisely timed inhibitory circuits—likely driven by OCs—that suppress subsequent auditory responses, enhancing temporal contrast and contributing to auditory scene analysis. 1. Pollak, G. D., et al., Hear. Res. 273, 134–144 (2011). 2. Oertel, D., et al., Proc. Natl. Acad. Sci. 97, 11773–11779 (2000).