Yes, we can hear while we sleep, though the process differs from conscious hearing during wakefulness. Our brains remain active, processing auditory information even during rest. This allows for a balance between achieving restorative sleep and maintaining awareness of our surroundings.
Brain Activity During Sleep
The brain processes sound during sleep, but its response differs from wakefulness. Sounds reach the brain, but their processing changes across sleep stages. In non-rapid eye movement (NREM) sleep, especially deep stages like N3, the brain’s responsiveness to external stimuli weakens.
Basic sound processing remains active in regions like the brainstem. The auditory cortex also remains active, but its connectivity with other brain regions, like the thalamus, decreases as sleep deepens. This reduced coordination means the brain may not fully process or consciously recognize sounds, even when receiving auditory input.
The Brain’s Selective Auditory Filter
The brain acts as a filter, allowing certain sounds to penetrate sleep while ignoring others. This selective processing prioritizes sounds deemed important or potentially threatening. For instance, sounds like a baby crying, one’s name, or an alarm are more likely to trigger a response and awaken a person than continuous background noise.
The reticular activating system (RAS), a network of nerves in the brainstem, partly manages this filtering by regulating wakefulness and attention. The RAS filters out unnecessary sensory information, allowing the brain to focus on important stimuli. Sounds indicating danger, such as screams or alarms, can directly activate the amygdala, a brain region involved in emotional reactions and attention, even during sleep. This selective processing highlights the brain’s ability to balance sleep with environmental monitoring.
How Sound Affects Sleep Quality
Even if sounds don’t cause full awakening, they can still significantly affect sleep quality. Noise can lead to micro-arousals: brief awakenings that may not be consciously remembered but disrupt the sleep cycle. These disruptions can fragment sleep, reducing time in restorative deep and REM sleep, and increasing time in lighter stages.
Chronic sleep disruption from noise can have several consequences. Individuals may experience increased daytime fatigue, irritability, and impaired cognitive function, including reduced attention and concentration. Long-term noise exposure during sleep has also been associated with health implications, such as elevated heart rate, blood pressure, increased stress hormone production, and a possible link to cardiovascular issues.
Creating a Quieter Sleep Environment
To minimize sound disturbances and improve sleep quality, several strategies can be implemented. Earplugs or noise-canceling headphones can effectively block external sounds. White noise machines, which produce consistent sound, can mask disruptive noises and create a more peaceful sleeping environment.
Soundproofing techniques can also reduce noise intrusion. Sealing gaps and cracks around windows and doors with weather stripping prevents sound from entering. Heavy curtains or drapes absorb sound. Arranging furniture, such as placing heavy bookshelves against shared walls, can further block noise. Adding rugs or carpets to hard floors can also absorb sound within the room.