Longitudinal monitoring of developmental plasticity in the mouse auditory cortex

The postnatal brain undergoes substantial plasticity in order to represent features and statistics of the sensory world. To date, for technical reasons it has been difficult to examine experience-dependent changes over the course of postnatal development. Here we perform longitudinal two-photon calcium imaging of hundreds of neurons in the auditory cortex of young mice, from postnatal day (P) 12 into adulthood. Auditory cortical neurons started responding to tonal stimuli by P13-14 with an initial tonotopic organization that expanded over the next few days. We documented the daily variation in tuning curves and best frequency, and while some neurons gradually changed their frequency representation across days, altogether our findings support the functional maturation of a largely stable auditory map at the population level. We then compared the representation of mouse pup ultrasonic vocalizations to pure tone responses. Ultrasonic pure tone tuning developed with a delay, coinciding with emerging responses to ultrasonic vocalizations. Vocalization responses initially were observed in neurons tuned to ultrasonic frequencies, but over later development the vocalization responses became independent from ultrasonic frequency tuning. Our results show how varied sensory representations at the single-cell and population levels in the postnatal auditory cortex emerge and change over the course of early-life development.