DEVELOPMENTAL PLASTICITY AND SENSORY EXPERIENCE SHAPE ADULT CODING AND PERCEPTION OF SOUND INTENSITY AND ITS MODULATION

Detecting moving objects or understanding speech depends on the ability to perceive sound intensity and its modulation. How these functions are shaped by developmental plasticity and sensory experience remains unclear. In our study, we address this knowledge gap combining behavioral tests with in-vivo electrophysiological recordings in the primary auditory cortex (A1) of mice. We first silenced A1 using optogenetics in behavioral tasks, confirming its role in processing intensity-modulated sounds (IMS), but not constant-intensity sounds (ICS). We then examined the neuronal activity in response to ICS and IMS in juvenile (postnatal day 30; P30) and adult mice (>P55). We found that neurons are tuned to specific sound intensities and selectively respond to IMS. In juvenile mice, most neurons are tuned to higher intensities, and respond to up-IMS by increasing their spike rate and down-IMS by decreasing it, tracking dynamic changes of sound intensity. Surprisingly, in adult mice most neurons are tuned to lower intensities and respond to up-IMS by counterintuitively decreasing their spike rate and down-IMS by increasing it. Finally, we studied how sensory experience during development shapes cortical function in adulthood by exposing mice to down-IMS during different developmental time windows. We found alterations in ICS and IMS processing, and in the discrimination ability between ICS and IMS only in mice exposed between P31-P38, identifying this time window as the critical period for IMS. These results highlight how sensory experience during development shapes complex cortical function, with potential implications for the pathophysiology of neurodevelopmental and psychiatric disorders.