Pregnant women are often warned to stay away from drugs, cigarettes, and alcohol during pregnancy. But when a mother's addiction is too strong, her child can suffer dire consequences.

The March of Dimes, an initiative begun 75 years ago to ensure the health of all newborns, warns mothers against smoking during pregnancy, as they are more likely to have children with birth defects, learning disabilities, and respiratory issues. The Centers for Disease Control and Prevention (CDC) agrees that smoking leads to pregnancy complications, premature births, and stillborn children.

Nicotine and other drugs work on the brain's pleasure centers, stimulating them and creating feelings of ease and calm in users. However, when a mother uses a drug like nicotine, both her and her baby's pleasure centers are being stimulated. To have such high amounts of stimulation in pleasure centers in the brain before birth should have some effect on the child's life afterward.

A new study indicates that exposure to maternal cigarette smoking, while it may cause defects and poor health, can also cause an altered state of reward processing in children, especially in their teen years. Altered reward processing in these children indicates a need to participate in risky behaviors, like unsafe driving or drug use or abuse, for the pleasure they feel afterward. In a study of 177 teens aged 13 to 15 who had been exposed to cigarettes prenatally, researchers found that exposed teens were more impulsive than non-exposed teens and were more likely to be excited by exploring new things, drugs included. On the note of substance use and abuse, five percent of those teens admitted to having smoked cigarettes in the 30 days prior to their evaluations, eight percent of them had the likelihood to develop alcohol abuse, and 45 percent had smoked at least one cigarette in their life. While there is some degree of free will here, 32 percent of the non-exposed teens had smoked at least one cigarette in their lifetime, compared to 45 percent in exposed teens - the differences in likelihood to develop drug abuse problems are clear.

The teens were given tasks during which their reaction times to monetary incentives were measured. They were instructed to push a button when a figure popped up onto a screen, and were told of the monetary amount rewarded if they pushed the button quickly enough beforehand in order to measure how the incentive would affect their activity. The experiment showed that there was little dose-dependent relationship based on the amount of maternal cigarette smoking the teen had endured as a fetus, because the majority of the teens with fetal exposure to cigarettes became very excited and impulsive with their button pushing when there was a reward involved, and many reacted negatively when they were not successful at their task. The majority of the exposed teens tended to push the button too late, and therefore would not get a reward, but clearly, there was a disconnect between their understanding of the visual stimulus and creation of a motor response. The receipt of reward made no difference in response to exposed and unexposed teens, as they reacted similarly. However, the anticipation of the impending reward increased reaction times, but not accuracy, of the exposed teens significantly, especially when a large reward was promised.

The researchers conjecture that prenatal exposure to nicotine alters brain structure in a way that lowers levels of neurotransmitters that cause pleasurable feelings in the brain, like dopamine. This indicates that these children's brains do not have enough dopamine in them to give them enough pleasurable feelings, and so they act in ways to increase pleasure, by using drugs for instance.

Researchers also found that mothers who continued to smoke during pregnancy had an average of seven cigarettes per day. This finding, along with the findings about teens, indicates a serious need to stop future mothers from smoking.

The CDC reports that 13 percent of American women smoked during their pregnancy. However, they also report that 45 percent of women successfully quit smoking during a pregnancy to ensure the health of their child. The researchers encourage doctors to tell women about the risk for their child's drug use and development of addiction to get women to stop smoking.

Source: Muller KU, Menningen E, Ripke S, et al. Altered Reward Processing in Adolescents With Prenatal Exposure to Maternal Cigarette Smoking. JAMA. 2013.