Spontaneous calcium signalling in the developing mammalian cochlea

In mammals, the accurate and high-fidelity representation of sound largely depends on the cochlea, the sensory organ specialized for transducing acoustic signals into neural activity with remarkable temporal precision. Prior to hearing onset, which occurs around postnatal day 12 in most altricial rodents, the immature cochlea plays an active role in the refinement of neural circuits along the auditory pathway. To accomplish this function, sensory hair cells and glia-like supporting cells in the immature cochlea generate distinct patterns of spontaneous Ca2+ signals. Synchronized Ca2+-dependent activity across multiple hair cells is conveyed to the ascending auditory neurons, where it contributes to the emergence of tonotopic maps that enable frequency discrimination. Within the cochlea itself, this spontaneous Ca2+ activity serves to promote cellular and synaptic refinement. In this review, we summarize the current insights into the cellular and molecular mechanisms responsible for generating and modulating these spontaneous Ca2+ signals in the developing cochlea, and how they regulate the activation of auditory afferent fibres.