Abstract
Sound recognition relies not only on spectral cues, but also on temporal cues, as demonstrated by the profound impact of time reversals on perception of common sounds. To address the coding principles underlying such auditory asymmetries, we recorded a large sample of auditory cortex neurons using two-photon calcium imaging in awake mice, while playing sounds ramping up or down in intensity. We observed clear asymmetries in cortical population responses, including stronger cortical activity for up-ramping sounds, which matches perceptual saliency assessments in mice and previous measures in humans. Analysis of cortical activity patterns revealed that auditory cortex implements a map of spatially clustered neuronal ensembles, detecting specific combinations of spectral and intensity modulation features. Comparing different models, we show that cortical responses result from multi-layered nonlinearities, which, contrary to standard receptive field models of auditory cortex function, build divergent representations of sounds with similar spectral content, but different temporal structure.
Highlights
Sound recognition relies on spectral cues, and on temporal cues, as demonstrated by the profound impact of time reversals on perception of common sounds
We combined two-photon calcium-imaging experiments and behavioural assays to show that the positive bias for up-ramping sounds, as compared with down-ramping sounds is present in mice at both the cortical and perceptual level, indicating that this is a general property of the mammalian auditory system
We show that the mechanism underlying the observed perceptual asymmetry is most likely the sequence of nonlinearities implemented in the multi-layered architecture of the auditory system to extract divergent, high-level representations of intensity-modulated sounds
Summary
Sound recognition relies on spectral cues, and on temporal cues, as demonstrated by the profound impact of time reversals on perception of common sounds. Recent single neuron recordings in cat auditory cortex have suggested the existence of a positive bias for up-ramps in non-primates, this study focused only on very short ramps and found a bias only for the duration of cortical responses[19] All these results suggest a coding asymmetry between up- and down-ramps, the representation principles of intensitymodulated sounds in auditory cortex and the computational underpinnings of asymmetric responses to sounds are largely unknown, despite their pivotal relevance to the understanding of natural sound perception. We combined two-photon calcium-imaging experiments and behavioural assays to show that the positive bias for up-ramping sounds, as compared with down-ramping sounds is present in mice at both the cortical and perceptual level, indicating that this is a general property of the mammalian auditory system We demonstrate that this bias is the result of profound nonlinearities that go beyond sensory adaptation mechanisms. We show that the mechanism underlying the observed perceptual asymmetry is most likely the sequence of nonlinearities implemented in the multi-layered architecture of the auditory system to extract divergent, high-level representations of intensity-modulated sounds
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