Smoking while pregnant may be linked to less control over inhibitions when the child is an adult, a new study that looked at brain scans suggests. People whose mothers smoked during pregnancy had weaker responses in the regions of their brains known to be involved in inhibition control, compared to those whose mothers didn’t smoke, researchers found.

Smoking while pregnant has been tied to attention-deficit/hyperactivity disorder, or ADHD, among kids. Children with the condition usually have trouble concentrating and controlling their impulses.

The researchers used special magnetic resonance imaging (MRI) scans to see what activity was going on in the young adults’ brains when they were given a test to measure their control over inhibitions.

They found that the brains of the 38 young adults with mothers who smoked during pregnancy didn’t show as much of a response in the areas that are important to inhibition control as those of the 140 people with non-smoking mothers.