The study included 12 healthy, full-term infants born to mothers who smoked an average of 15 cigarettes a day.

The study also identified a dose-dependent relationship between cortical activation rates and levels of infant urinary cotinine, a nicotine metabolite. Decreased cortical arousals from sleep have been observed in infants who later died of SIDS, noted senior investigator Kerry Horne, scientific director of the Krisha Centre for Baby Health Research at Monash University in Melbourne. Infants with the highest levels of smoke exposure had the lowest levels of cortical arousal. They also had lower rates of full cortical arousals from sleep and higher rates of sub-cortical activations than infants of nonsmoking mothers.

The results sho that infants who had been exposed to smoke had reduced sub-cortical activation to cortical arousal. At 2 to 4 weeks of age, 2 to 3 months, and 5 to 6 months. They found that when mothers smoke, the sleep arousal process of infants, which awakens them in response to a life-threatening situation, is altered, increasing the risk for SIDS.

All the children were assessed three times.

The infants' arousal responses during daytime sleep were compared with those of 13 healthy infants of nonsmoking mothers.