Enhanced corticobulbar excitability in chronic smokers during visual exposure to cigarette smoking cues

Motor excitability in chronic smokers and nonsmoking controls. (A) Interaction between motor evoked potentials (MEPs) and visual cue factors in the nicotine withdrawal condition. Histograms show that in chronic smokers, but not controls, tongue MEPs were significantly enhanced during the presentation of smoking cues compared to scrambled stimuli. No effect was reported for the extensor carpi radialis (ECR) MEPs in chronic smokers or for both tongue and ECR MEPs in the control group. (B) Interaction between muscle and visual cue factors in the nicotine intake condition. Histograms show no difference in the excitability of both tongue and ECR muscles among the groups during the exposure to visual cues (smoking cue v. scrambled stimulus). (C) Condition × muscle × stimulus interactions in chronic smokers under withdrawl and intake conditions. Histograms show enhanced tongue muscle excitability under the withdrawal condition during the exposure to smoking cues compared to scrambled stimuli. This difference disappeared after participants smoked a nicotine or placebo cigarette (i.e. intake condition). Moreover, tongue MEPs during exposure to smoking cues were significantly enhanced under the withdrawl condition compared to the intake condition. Conversely, tongue MEPs during the exposure to scrambled stimuli were significantly reduced under the withdrawl condition compared to the intake condition. The ECR MEP amplitudes were identical in both the withdrawal and intake conditions. Raw MEPs were converted to z scores. Vertical bars indicate standard error of mean. *p < 0.05.