Early postnatal noise exposure degrades the stimulus-specific adaptation of neurons in the rat auditory cortex in adulthood.

Many auditory cortical neurons exhibit stimulus-specific adaptation (SSA), i.e., they respond weakly to frequently occurring stimuli but strongly to the same stimuli when presented rarely. SSA has been proposed to be a potential mechanism to engage deviance detection or novelty detection. Previous studies on SSA were investigated in animals reared in normal environment. It has been shown that early postnatal noise exposure impairs the development of cortical processing of sound information. However, it is not understood whether postnatal middle-level noise exposure affects the SSA in the primary auditory cortex (AI), and if yes, whether the impacts of noise exposure on SSA varied with noise exposure periods. Here we used a frequency oddball paradigm to determine the SSA of AI neurons in three groups of rats: the control rats were reared in normal environment without noise exposure, the young noise-exposed rats received a 70 dB SPL white noise exposure from P10 to P56, and the adult noise-exposed rats received the same noise exposure from P57 to P103. We found that early postnatal noise exposure reduced the proportion of SSA neurons in AI and decreased the strength of SSA of AI neurons in the young noise-exposed rats in adulthood. In contrast, the same noise exposure to adult rats had no significant impacts on the SSA of AI neurons in adult noise-exposed rats. The results suggest that environmental noise might be a risk factor for abnormal postnatal development of cortical processing of frequency deviance in a sound sequence.