Edythe London, study leader and a professor of psychiatry at the Semel Institute for Neuroscience and Human Behavior at UCLA, along with a team of researchers from UCLA and the University of Texas at Austin, have found that teenage smokers have reduced brain activity compared to non-smokers. 

The UCLA team determined these results by measuring the level of nicotine dependence in 25 smokers and 25 non-smokers that ranged from ages 15 to 21 through the use of the Heaviness of Smoking Index (HSI). The HSI looks at how many cigarettes the teen smokes per day and how soon they begin smoking each day to determine their dependence. 

Researchers then performed a test called the Stop-Signal Task (SST) on the participants. While being subjected to functional magnetic resonance imaging (fMRI), the test subjects were asked to press a button as quickly as they could when a lighted arrow appeared. The only time they were not to press the button was when an auditory cue was played. This tested each participant’s ability to inhibit an action. 

London described the results as "interesting." Higher HSI measurements, or the more a teen smoked, resulted in reduced activity in a part of the brain known as the prefrontal cortex, which is responsible for decision-making. But despite this reduced activity, both smokers and non-smokers performed about the same in the Stop-Signal Task. 

"The finding that there was little difference on the Stop-Signal Task between smokers and non-smokers was a surprise," said London. "That suggested to us that the motor response of smokers may be maintained through some kind of compensation from other brain areas." 

According to the study, the fact that both smokers and non-smokers performed the same in the Stop-Signal Task "suggests that early interventions during the teen years" may prevent teens from smoking occasionally to smoking heavily.  

London also noted that protracted development of the prefrontal cortex may cause poor decision-making in teenagers, due to immature cognitive control during the time of adolescence.  

"Such an effect can influence the ability of youth to make rational decisions regarding their well-being, and that includes the decision to stop smoking," said London. "As the prefrontal cortex continues to develop during the critical period of adolescence, smoking may influence the trajectory of brain development, affecting the function of the prefrontal cortex. In turn, if the prefrontal cortex is negatively impacted, a teen may be more likely to start smoking and to keep smoking - instead of making the decision that would favor in a healthier life."

This study was published in Neuropsychopharmacology.