Smoking, nicotine dose and the lateralisation of electrocortical activity.

The effects of cigarette smoking on the balance of activity of the cerebral hemispheres were studied in two experiments. Experiment 1 examined the effects of smoking on lateralisation of EEG alpha and beta power in six male smokers, and revealed a dose-related biphasic action. Low doses of nicotine as measured by residual butt analysis increased left hemisphere activity in a dose related manner, while higher doses (greater than 1.1 mg) reversed this effect. Experiment 2 examined the time course of the changes in EEG alpha, beta, theta and delta lateralisation in 11 male smokers. During the initial period of smoking there was a reduction in EEG alpha, reflecting cortical activation, followed by an increased in alpha power towards the end of the cigarette. These changes were accompanied in smokers taking moderate nicotine doses, by an initial shift towards left hemisphere activation, followed by a reduction in left hemisphere activation relative to the right. Initial changes in delta and theta power were negatively correlated with nicotine dose. Higher nicotine doses were associated with greater shifts towards right hemisphere activation, as indicated by beta and delta lateralisation, and also with greater decreases in subjective arousal. These results were interpreted as supporting the hypothesis that the stimulant action of lower doses of nicotine involves the activation of a left hemisphere "Go" system, while the sedative effect of higher doses involves increased activation of the right hemisphere "NoGo" system.