A new study shows that nicotine builds up in the brain over the course of smoking a whole cigarette.

Researchers at Duke University Medical Center put to rest the idea that each puff on a cigarette causes a spike of nicotine to the brain.

In fact, it takes a while for the nicotine to reach its peak effect.

The researchers used a PET scan on 13 addicted smokers and ten non-addicted smokers to see which parts of the brain lit up and when.

The addicts took longer to get all the nicotine up to their brains, which surprised researchers.

Researchers theorize that it's because the nicotine lingers longer in their damaged lungs.

The bottom line was that both the addicted and non-addicted smokers ended up with similar amounts of the stimulant in their brains.

The Duke researchers don't have any good answers why some people are more prone to being addicted to smoking than others.

The study is published in the journal Proceedings of the National Academy of Sciences.