Distinct higher-order representations of natural sounds in human and ferret auditory cortex

Little is known about how neural representations of natural stimuli differ across species. Speech and music for example play a unique role in human hearing, but it is unclear how auditory representations of speech and music differ between humans and other animals. Using functional Ultrasound imaging, we measured responses in ferret auditory cortex to a set of natural and spectrotemporally-matched synthetic sounds previously tested in humans, as well as natural and synthetic ferret vocalizations. Ferrets showed similar frequency and modulation tuning to that observed in humans. But while humans showed selective responses to natural speech and music in non-primary auditory cortex, ferret responses to natural and synthetic sounds were closely matched throughout primary and non-primary regions, even when tested with ferret vocalizations. This finding suggests the unique demands of speech and music have substantially altered higher-order acoustic representations in human auditory cortex, while largely preserving lower-level tuning for frequency and modulation.