The influence of smoking on reward responsiveness and cognitive functions: a natural experiment.
To investigate the effects of (a) nicotine abstinence and (b) cigarette smoking after abstinence, on reward responsiveness and cognitive functions which are putatively dependent on activity in the dopaminergic system implicated in smoking. During Ramadhan, Muslim smokers elected to abstain from smoking either for the whole month (RAMQUIT) or during daylight hours (DAYQUIT). These groups, and non-smokers (NOSMOKE), were assessed on two occasions 6 hours apart (TEST1 and TEST2). DAYQUIT participants had abstained for 6 hours at TEST1 and smoked a single cigarette immediately prior to TEST2. RAMQUIT participants had abstained for at least 10 days prior to TEST1 and remained abstinent at TEST2. NOSMOKE and RAMQUIT participants are a small snack prior to TEST2 to control for non-specific consummatory effects. TEST1 was conducted at the mosque and TEST2 in participants' homes. All were male; mean age was 26.7 years. Modal cigarette consumption prior to Ramadhan by both the 13 DAYQUIT and the 11 RAMQUIT smokers was 21-30 per day. DAYQUIT subjects rated themselves as more dependent. The Card Arranging Reward Responsivity Objective Test (CARROT), testing behavioural responsiveness to small financial incentive; digit span, measuring attention; verbal fluency, indexing frontal lobe function; and the two-choice guessing test (2CGT; at TEST1 only), measuring response stereotypy. At TEST1, compared with non-smokers, both smoking groups showed greater stereotypy (2CG) and lower reward responsiveness (CARROT). DAYQUIT participants improved on all measures after smoking a single cigarette. No marked changes were seen in the other groups. These data suggest that (i) abstaining smokers have impaired dopaminergic function and (ii) nicotine consumption may boost their dopaminergic activity.