Impulsive behavior in preteens linked to mom's smoking when pregnant.

May 26, 2009

Bennett, DS, FB Mohamed, DP Carmody, M Bendersky, S Patel, M Khorrami, SH Faro, and M Lewis. 2009. Response inhibition among early adolescents prenatally exposed to tobacco: An fMRI study. Neurotoxicology and Teratology doi:10.1016/

Synopsis by Wendy Hessler and Paul Eubig, DVM

New research indicates that smoking during pregnancy can lead to impulsive behavior in children. Preteenagers whose mothers smoked during pregnancy are more impulsive on a standard behavior test and use different regions of their brain while performing the test when compared to children whose mothers did not smoke. The study highlights how early exposure to cigarette smoke can alter brain development and affect lifelong behaviors and thinking patterns. The changes to brain function found were similar to those seen in children with attention deficit-hyperactivity disorder (ADHD).


Research has demonstrated that smoking during pregnancy can have long-lasting effects on the child. These can include physical changes at birth, such as low birth weight, and lifelong consequences, such as decreased lung function, weight gain and altered behaviors, including aggression and ADHD (Neuman et al.  2007).

Still many women continue to smoke during their pregnancy, possibly affecting their children's long term health (NSDUH 2007).

Although the brain continues maturing until a child is well older than 20 years of age, the basic layout of the brain is established while the child is still in the womb.  It is during this sensitive period of brain development that prenatal smoking can cause harm. 

While there are numerous chemicals in cigarette smoke, nicotine is a likely cause for many of the long lasting changes. 

There are several ways that prenatal exposure to nicotine can affect the brain and lead to permanent changes. Nicotine can interfere with the normal way that some types of nerve cells (neurons) communicate with each other via chemical neurotransmitters across synapses. Nicotine can also alter the growth and development of neurons as well as kill some neurons.

Attention deficit-hyperactivity disorder is a common childhood behavioral disorder that is characterized by over activity, problems focusing and paying attention and impulsive actions. About 10 percent of 9-12-year-olds are diagnosed as ADHD, according to the Centers for Disease Control and Prevention (CDC 2009). Experts believe the condition my be brought on by a combination of genetics and exposure to environmental triggers.

What did they do?

A team of scientists compared differences in the brain activation patterns of two groups of 12-year-old children performing a behavior task called Go/No-Go. One group was born to mothers who smoked  during pregnancy while the other group was born to mothers who did not.

A non-invasive brain imaging technique called functional MRI – fMRI for short – determined which parts of the brain were activated during the testing. The instruments can detect oxygen increases that signal which areas of the brain are being used. fMRIs are similar to MRIs that hospitals use to diagnose a patient's health problems.

The Go/No-Go task is a simple test of the ability to withhold a response to a signal. In this task, children watch a screen on which random letters of the alphabet appear. They are asked to push a button whenever they see a letter (Go trial). However, they are instructed not to push the button when the letter “V” appears (No-Go trial).

This is more difficult than it sounds. The letter “V” only appears about 25 percent of the time, so the children tend to push the button even when it appears.

Children whose mothers smoked during pregnancy pushed the button during No-Go trials 31 percent more often than children whose mothers did not smoke. This suggests that prenatal exposure to cigarette smoke contributes to impulsive-type behavior. 

Of even more interest were the differences found in the brain regions that the two groups used. The children whose mothers smoked used more regions of their brains during the task, a feature of less mature, developed brains. This occurred even when the child responded correctly. 

The researchers also examined the role of factors including current smoke exposure, intelligence and the mother’s use of alcohol while pregnant that might have contributed to the changes seen. However, none of these factors were found to be significant.

Profound behavior and brain differences were found in preteen children who were exposed to cigarette smoke before they were born. They used more regions of their brains and were less able to restrain their actions during a standard test of impulsive behavior. Similar physical and behavioral are seen in children with ADHD.

The findings suggest that prenatal exposure to cigarette smoke results in impulsive-type behavior since this task evaluates response inhibition or the ability to override the tendency to respond to a signal.

Additionally, the study suggests that the brains of these children are less mature. Typically, younger children have a similar broad pattern of brain activation while performing the Go/No-Go task. As the children mature their brains become more efficient and only activate a more limited number of areas in the brain while performing the task. Yet the brains of the adolescents prenatally exposed to tobacco resembled the brains of younger children in how they processed the task.

This study builds on prior research that also demonstrates poor impulse control in children whose mothers smoked during pregnancy. Yet it went farther by evaluating the activation pattern in the brain of the children while they were performing a task of response inhibition.

It should be noted that children with ADHD also perform poorly on the Go/No-Go task and have a similar pattern of brain activation to that of the tobacco exposed children in this study. The role of tobacco exposure in the womb to the development of neurobehavioral disorders such as ADHD is currently being studied by several different research groups.

While this study did not tease out what component of the cigarette smoke influenced the changes, prior studies suggest nicotine is a culprit. Nicotine affects the brain in several ways. All of them can have long-lasting implications, as this study shows.

One of the short comings of the study was the small number of children involved: 7 in the exposed group and 11 in the non-exposed group. However these significant findings will hopefully lead to larger studies in the future.


Attention-Deficit / Hyperactivity Disorder (ADHD). 2009. Centers for Disease Control and Prevention. Web site accessed May 18, 2009.

Functional MR Imaging (fMRI) - Brain.

Neuman, RJ, E Lobosa, W Reicha, CA Hendersona, L-W Suna and RD Todd. 2007. Prenatal smoking exposure and dopaminergic genotypes interact to cause a severe ADHD subtype. Biological Psychiatry 61:1320-1328.

NSDUH. Cigarette use among pregnant women and recent mothers. 2007. Office of Applied Studies. National Survey on Drug Use and Health: Substance Abuse and Mental Health Services Administration, Rockville, MD.

Pregnant? Don't Smoke! Centers for Disease Control and Prevention.

Prenatal smoking increases ADHD risk in some children. Science Daily April 11 2007.




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