Transient Hearing Loss Within a Critical Period Causes Persistent Changes to Cellular Properties in Adult Auditory Cortex.

Sensory deprivation can induce profound changes to central processing during developmental critical periods (CPs), and the recovery of normal function is maximal if the sensory input is restored during these epochs. Therefore, we asked whether mild and transient hearing loss (HL) during discrete CPs could induce changes to cortical cellular physiology. Electrical and inhibitory synaptic properties were obtained from auditory cortex pyramidal neurons using whole-cell recordings after bilateral earplug insertion or following earplug removal. Varying the age of HL onset revealed brief CPs of vulnerability for membrane and firing properties, as well as, inhibitory synaptic currents. These CPs closed 1 week after ear canal opening on postnatal day (P) 18. To examine whether the cellular properties could recover from HL, earplugs were removed prior to (P17) or after (P23), the closure of these CPs. The earlier age of hearing restoration led to greater recovery of cellular function, but firing rate remained disrupted. When earplugs were removed after the closure of these CPs, several changes persisted into adulthood. Therefore, long-lasting cellular deficits that emerge from transient deprivation during a CP may contribute to delayed acquisition of auditory skills in children who experience temporary HL.