The effects on sleep play a critical role in the long-term health consequences of noise exposure

Sleep is a very dangerous state from an evolutionary perspective as we are unconscious and it takes time to arouse from sleep and react to threats in a meaningful way. Thus, it is not surprising that our full sensory array continues to monitor our environment during sleep, always ready to wake us up (although with different sensitivity depending on sleep stage). In fact, the multiple brief awakenings a healthy sleeper experiences during the night [1] can be thought of as “brief checks” into our sleep environment. As a long-range sensor, the auditory system plays a critical role in monitoring the environment during sleep. It analyzes not only sound levels but also sound content during sleep [2]. The thalamus has a gating function, shielding the cortex from sensory content deemed irrelevant, often associated with a K-complex in the electroencephalogram [3]. We do habituate to noise, but still react to individual noise events during sleep even after long exposure periods (i.e. years), albeit with lower probabilities. Compared to cortical arousals, autonomic arousals habituate to a much lesser degree with likely implications for long-term health consequences (see below) [4].