Developmental encoding of ultrasound vocalizations in the mouse auditory cortex

Mice communicate through high-frequency ultrasound vocalizations (USVs), which are crucial for social interactions such as courtship and aggression. Although USV representation has been found in adult brain areas along the auditory pathway, including the auditory cortex (ACx), no evidence is available on the neuronal representation of USVs early in life. Using in vivo two-photon calcium imaging, we analyzed ACx layer 2/3 neuronal responses to USVs, pure tones (4-90 kHz), and high-frequency modulated sweeps from postnatal day 12 (P12) to P21. We found that ACx neurons are tuned to respond to USV syllables as early as P12-P13, with an increasing number of responsive cells as the mouse age. By P14, while pure tone responses showed a frequency preference, no syllable preference was observed. Additionally, at P14, USVs, pure tones, and modulated sweeps activate clusters of largely non-overlapping responsive neurons. Finally, we show that while cell correlation decreases with increasing processing of peripheral auditory stimuli, neurons responding to the same stimulus maintain highly correlated spontaneous activity after circuits have attained mature organization, forming neuronal sub-networks sharing similar functional properties.