Sound asleep: sensory decoupling during sleep depends on an infant's sensory profile.

Initiating and maintaining sleep requires gating of sensory input. Sensory processing differences, such as elevated sensory reactivity, have emerged as a potential driver of sleep difficulties in autism. Both sensory and sleep difficulties are prevalent in autistic individuals and emerge early in development. Here, we use polysomnography to understand how infant sensory reactivity affects the ability to maintain sleep in a quiet or noisy environment. Forty-four 8- to 11-month-old infants at typical and elevated likelihood for autism participated in a lab-based nap study consisting of two counterbalanced visits, a baseline and an auditory stimulation condition. In the stimulation condition, 60 dB pure tones were played during sleep. We measured slow waves and sleep spindles, electroencephalogram features previously linked to the ability to protect sleep from sensory disturbance. We show that higher caregiver-reported sensory reactivity was significantly associated with lower slow wave activity and density, across both nap conditions. In the stimulation condition, infants with elevated sensory reactivity had even further decreased slow wave density and lower sleep spindle density. Comparisons of pre- and poststimulus windows showed that, rather than triggering immediate event-related disruptions, auditory input and sensory reactivity alter sleep microstructure across the longer timescale of the entire nap. Thus, highly reactive infants experience disruptions in their ability to enter or maintain periods of sensory disconnection, accentuated by the presence of auditory noise.