system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:When you're asleep, what part of the brain filters the noises you hear, determining whether to wake up or not?
gpt
When we sleep, we are inhibiting loads of different parts of the brain, so a stronger stimulus is required to activate them. 

Think of it like this - when we are awake there is a copper wire between the auditory centre of the brain and the higher centres of our brain that process and understand this auditory information and then respond to it. Copper is a very conductive metal, so even a very small voltage will mean that electricity passes through this circuit. 

When we go to sleep, this copper wire is switched out with a lead wire. Now lead can still conduct electricity, but it is much less conductive than copper. This means that a much higher voltage is required to get any activity in the circuit. Standard, background sounds of the night are unlikely to provide a big enough voltage to get a current to run though the wire. A really loud sound, however, will provide enough voltage and will wake us up. Other sounds that have very strong associations in our memory, e.g. our ringtone, alarm tone or a doorbell, may also provide enough voltage in the circuit even if they're a bit quieter.