How moderate levels of environmental noise — that is, noise that does not cause peripheral deficits in hearing — affect the adult brain is unclear. Here, rats continuously exposed to moderate structured noise (sound pressure of 65 dB) for 2 months showed an impaired ability to discriminate between sound stimulus rates in a behavioural task and deficits in the temporal processing of noise stimuli in the auditory cortex. Thus, in rats, levels of noise that do not affect the inner ear may still cause auditory function deficits.