What Distinguishes Light Sleepers?

Some people can sleep through anything, others see their sleep defeated by noise and other stimuli. A new study has identified a form of brain wave called a spindle measurable on an EEG that originates in the brain's thalamus that distinguishes the two kinds of people. Light sleepers have few spindle brave waves, while those who can sleep through anything have a lot. The activity in the thalamus associated with spindle brain waves blocks "disruptive sounds, touches or internal signals such as the oxygen content of the blood" that might otherwise wake sleepers, but does not block the sense of smell.