Your ears never sleep: auditory processing of nonwords during sleep in children

 

 

 

 

Adrienne Roman – adrienne.s.roman@vumc.org

Carlos Benitez – carlos.r.benitez@vanderbilt.edu

Alexandra Key – sasha.key@vanderbilt.edu

Anne Marie Tharpe – anne.m.tharpe@vumc.org

 

The brain needs a variety of stimulation from the environment to develop and grow. The ability for the brain to change as a result of sensory input and experiences is often referred to as experience-dependent plasticity. When children are young, their brains are more susceptible to experience-dependent plasticity (e.g., Kral, 2013) so the quantity and quality of input is important. Because our ears are always “on”, our auditory system receives a lot of input to process, especially while we are awake. But, what can we “hear” when we are asleep? And, does what we hear while we are asleep help our brains develop?

 

Although there has been research in infants and adults examining the extent to which our brains process sounds during sleep, very little research has focused on young children, a group that sleeps a significant portion of their day (Paruthi et al., 2016). We decided to start our investigation by trying to answer the question, do children process and retain information heard during sleep? To investigate this question, we used electroencephalography (EEG) to measure the electrical activity of children’s brains in response to different sounds – sounds they heard when asleep and sounds they heard when awake.

 

First, during the child’s regular naptime, each child was hooked up to a portable EEG. Using EEG, a technician could tell us when the child went to sleep. Once asleep, we played the child three made-up words over and over in random order for ten minutes. Then, we let the child continue to sleep until he or she woke up.

 

When the children awoke from their naps, we took them to our EEG lab for event-related potential (ERP) testing. ERPs are segments of on-going EEG recordings appearing as waveforms that reflect the brain’s response to  events or stimulation (such as a sound played).

 

The children wore “hats” consisting of 128 spongy electrodes while listening to the same three made-up words heard during the nap mixed in with new made-up words that the children never heard before. We then analyzed the ERPs, to determine if the children’s brains responded differently to the words played during sleep than to the new words the children had not heard before. We were looking for ‘memory traces’ in the EEG that would indicate that the children ‘remembered’ the words heard while sleeping.

 

We found that children’s brains were able to differentiate the nonsensical words “heard” during the nap from the brand new words played during the ERP testing. This means that the brain did not just filter the information coming in, but also retained it long enough to recognize it after they woke up. This is the first step in understanding the impact of a child’s auditory environment during sleep on the brain.

 

 

Kral, A. (2013). Auditory critical periods: a review from system’s perspective.

Neuroscience, 247, 117-133.

Paruthi, S., Brooks, L. J., D’Ambrosio, C., Hall, W. A., Kotagal, S., Lloyd, R. M.,

Malow, B. A., Maski, K., Nichols, C., Quan, S. F., Rosen, C. L., Troester, M. M., & Wise, M.S. (2016). Recommended amount of sleep for pediatric populations: a consensus statement of the American Academy of Sleep Medicine. Journal of clinical sleep medicine: JCSM: official publication of the American Academy of Sleep Medicine, 12(6), 785.

 

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