Smoking may thin the outer layer of the brain the cerebral cortex according to a new study.

The researchers scanned the brains of 22 smokers and 21 nonsmokers using magnetic resonance imaging (MRI). In the smokers, an area of the cortex known as the left medial orbitofrontal cortex was thinner. And the more a person smoked, the thinner this brain area was.

Changes to the orbitofrontal cortex have previously been linked to drug additions and compulsive behavior.

"Since the brain region in which we found the smoking-associated thinning has been related to impulse control, reward processing and decision-making, this might explain how nicotine addiction comes about," study researcher Simone Kühn said in a statement.

And because heavier smoking was linked to more pronounced thinning, the results "suggest that smoking may have a cumulative effect on the brain, said Dr. John Krystal, editor of Biological Psychiatry, the journal in which the study was published.

"This concerning finding highlights the importance of targeting young smokers for antismoking interventions," Krystal said.

While previous work has linked tobacco smoking with brain abnormalities, including brain decay, the new study is the first to look specifically at the habit's effect on cortical thickness, the researchers said. The cortex is involved in many of the brain's so-called "higher order functions," such as language and memory. A thinner cortex has previously been associated with normal aging and impaired cognition.

The researchers said they're planning future studies to examine the effects of quitting smoking on the brain.

The study is published in the Dec. 1 issue of the journal Biological Psychiatry.