Selectivity for animal vocalizations in the human auditory cortex

We aimed at testing the cortical representation of complex natural sounds within auditory cortex using human functional magnetic resonance imaging (fMRI). To this end, we employed 2 different paradigms in the same subjects: a block-design experiment was to provide a localization of areas involved in the processing of animal vocalizations, whereas an event-related fMRI adaptation experiment was to characterize the representation of animal vocalizations in the auditory cortex. During the first experiment, we presented subjects with recognizable and degraded animal vocalizations. We observed significantly stronger fMRI responses for animal vocalizations compared with the degraded stimuli along the bilateral superior temporal gyrus (STG). In the second experiment, we employed an event-related fMRI adaptation paradigm in which pairs of auditory stimuli were presented in 4 different conditions: 1) 2 identical animal vocalizations, 2) 2 different animal vocalizations, 3) an animal vocalization and its degraded control, and 4) an animal vocalization and a degraded control of a different sound. We observed significant fMRI adaptation effects within the left STG. Our data thus suggest that complex sounds such as animal vocalizations are represented in putatively nonprimary auditory cortex in the left STG. Their representation is probably based on their spectrotemporal dynamics rather than simple spectral features.