How does sound “stop” when you’re about to fall asleep? I’ve been sleeping with a fan on due to the heat and I noticed as I fall asleep, it sort of “cuts off” and not fades to silence. What stops it?

Question

Title really. If it just me that experiences this then I’ll be amazed

In: 182

Answer 1

Your brain has an incredible capability to filter out rhythmic and expected stimuli. Neurons generally function in 2 modes- make things more active (excitation) or make things less active (inhibition). When you fall asleep, your body is inhibiting a whole bunch of things, particularly your motor system- its because of this that sleep paralysis occurs, part of your cortex “wakes up” so that wakefulness & consciousness are occurring is but the inhibition on your motor system is still there so you can’t move.

To make this more “sound oriented,” an example of the brain filtering out expected noise – your own foot steps. People who get hearing aids and cochlear implants often complain of how loud their footsteps are! Its something we don’t consider because our brains have a LOT of experience filtering out those sounds, but its a very precisely tuned system. I imagine that these two system interact when you sleep- inhibition of auditory perception (neurons that fire when a sound happens and you can “perceive” it) and inhibition of neurons that are responding to the particular input that is “fan.”

​

FYI- falling asleep isn’t gradual. Its a distinct, marked moment.