Comparison of the brains of 22 smokers and 21 people who have never smoked in their lives has revealed that the left medial orbitofrontal cortex of the smokers was on average smaller than that of the non-smokers. Moreover, this reduction was greater the more cigarettes were smoked daily, and as a function of how long they had smoked. The region is involved in reward, impulse control, and decision-making, suggesting that fewer neurons there may mean you have to work harder for reward, and that your ability to curb your impulses and make decisions is impaired.
While it may be that smoking is affecting this damage, it may also be that those with a smaller orbitofrontal cortex are more likely to smoke (perhaps it is most likely that both are true!). Further research will need to distinguish these two possibilities.
(Submitted). Reduced Thickness of Medial Orbitofrontal Cortex in Smokers.
Biological Psychiatry. In Press, Corrected Proof,