For the research, study co-author Jeffrey Ellenbogen of Harvard Medical School recruited 12 self-described sound sleepers to spend three nights in his "comfy" lab.

The first night, the sleepers were treated to quiet conditions. But during the next two nights, scientists bombarded the subjects with several types of sounds—including jet engine roars and toilet flushes—after the people had fallen asleep. (Take National Geographic magazine's sleep quiz.)

Brain wave readings revealed that the more spindles a person had, the more likely he or she could stay asleep through the barrage of noises, Ellenbogen said.

(Related: "Naps Clear Brain's Inbox, Improve Learning.")

Everybody has spindles, which are controlled by the thalamus, a "way