Why smoking behind the bike sheds could harm your grades

Parents may now have another reason to worry about their children smoking. Nicotine may cause the teenage brain to develop abnormally, resulting in changes to the structure of white matter - the neural tissue through which signals are relayed. Teenagers who smoke, or whose mothers smoked during pregnancy, are also more likely to suffer from auditory attention deficits, meaning they find it harder to concentrate on what is being said when other things are happening at the same time.

Leslie Jacobsen of Yale University School of Medicine and colleagues used diffusion tensor imaging, which measures how water diffuses through brain tissue, to study the brains of 33 teenagers whose mothers had smoked during pregnancy. Twenty-five of the teens were daily smokers. The team also studied 34 teens whose mothers had not smoked, of whom 14 were daily smokers. ...

Earlier this year, Jacobsen's team reported that prenatal and teenage exposure to smoke were associated with reduced auditory and visual attention, with boys being particularly vulnerable to auditory deficits (Neuropsychopharmacology, DOI: 10.1038/sj.npp.1301398 ). In such boys, "the levels of disruption are significant enough that if you were already struggling at school it could tip you towards school failure," Jacobsen says. She now hopes to test whether the changes are reversible, by scanning the brains of teenagers who give up smoking.

David McAlpine, director of the Ear Institute at University College London, says the findings are interesting because the key brain pathway affected by nicotine helps determine how we process auditory information when distracted by other tasks. "The fact that smokers show changes in this pathway means they may be less able to hear what's being said," he says.

Nicotine binds to receptors in the brain that regulate neural development. Inappropriate stimulation could cause abnormal connections to form, says Jacobsen. Such misconnections are already thought to affect babies exposed to nicotine before birth, but this goes further: "The new findings show that there is a downstream effect on white matter - the magnitude of which is pretty remarkable," says Richard Todd at Washington University School of Medicine in St Louis, Missouri. "It seems the brain remains vulnerable long into adolescence."

•	Why smoking behind the bike sheds could harm your grades New Scientist (UK), Saturday, Jan. 5, 2008 Byline: Linda Geddes