Juvenile development of the mouse central auditory system

During development, neuronal circuits reshape and refine until auditory skills reach an adultlike
capability. Previous studies provided insights on this plasticity during the embryonic life
and the first two postnatal weeks of mouse development. Others investigated the role of
feedforward and feedback connectivity during adulthood. However, the developmental
plasticity of the auditory system during adolescence remained unclear. With this work, we
aimed at studying the processing of different sound features, from simple to more complex
sounds, during this developmental period in the central auditory system. We performed
electrophysiological recordings in head-fixed mice comprising the ages of adolescence -
postnatal day 20 (P20), P30, P40, and P50. Animals were passively exposed to different sound
protocols, including FMS and oddball sequence paradigms, and neural responses were
recorded from the central auditory areas - inferior colliculus (IC), medial geniculate body
(MGB), and primary auditory cortex (A1). We found MGB and A1 still maturing for deviance
detection during juvenile development (until P30 and ≥P50, respectively), while IC deviance
response seems to stabilize before P20. These results were not related to the common
adaptation to the standard tone (stimulus-specific adaptation) but rather to prediction error. A1
depends on experience for deviance detection maturation, and we found these changes to
relate to alterations in neuronal circuits of its deep layers. Corticothalamic projections were
also identified as implicated in the maturation of deviance detection in MGB. By exposing mice
to FMS during different time windows and performing recordings in A1, we identified the FMS
critical period during adolescence from P31 to P38. Other sensorial and molecular tools were
used to explore the dependency of the FMS critical period with the one for pure tones (P12-
P15). We found pure tone critical period acceleration or delay in time to not affect FMS critical
period. However, the FMS critical period only occurs if the pure tone critical occurs before.
Overall, our findings support the importance of juvenile plasticity for the refinement of
processing of some sound features while opening more questions for others, with the ultimate
goal of understanding how we make sense of sounds.