The breathing of us humans is an automatic action, it will happen whether we think about it or not, and no matter if we are asleep or awake. With dolphins, that’s not the case. As their breathing is always consciously done, you may wonder how they ever manage to give their brains the rest it needs to function properly.
The way a dolphin will handle this conundrum is by putting only half of the brain to sleep while the other one stays conscious, periodically alternating sides.
This way they are always alert enough to periodically swim to the surface for air.