This study provides evidence for a working memory deficit associated with acute withdrawal in a sample of smokers with a moderate severity of nicotine dependence. Smokers after ≥13 h abstinence, but not in satiety, performed more poorly on the N-Back Task than did non-smokers. More directly, working memory performance by smokers was significantly slower, especially in the 2-back condition, and more prone to errors when the participants had abstained >13 h as compared to when they were in relative satiety. These data support the conclusion that cessation of smoking produces impairments in working memory. Such deficits, in turn, may contribute to the maintenance of smoking behavior.
Although we found a performance deficit in smokers compared to non-smokers, the impairment we saw appeared to be due to abstinence from smoking. An earlier study however, reported that smokers who were abstinent for >12 h had slower responses but demonstrated no difference in errors compared with non-smokers (Ernst et al., 2001a). In contrast, we found that abstinent smokers (>13 h) showed significant deficits in accuracy but not reaction time compared to non-smokers. Also, the abstinent smokers (≥13 h) responded with less speed and less accuracy than when at satiety. The present observations suggest that impaired performance reflects abstinence and is not a trait-like phenomenon.
Although the truncation of the data had minimal impact on the statistical inferences made, there is no guarantee that the effect of the data loss in the main study is the same as that observed in the subsample. However, particularly with respect to the observed effect of withdrawal on reaction times, it is difficult to envision a scenario in which the data truncation would effectively create, or even enhance a true difference across conditions.
Anticipating a deleterious effect of abstinence from smoking on performance of the N
-Back Task, we tested for possible improvement from smoking a cigarette. Although nicotine gum previously produced no effect on performance in abstinent smokers (Ernst et al., 2001a), we reasoned that smoking might be effective, as components of the smoking experience, other than nicotine per se, influence behavior. In this regard, nicotine patches and gum do not reduce craving as well as smoking a cigarette (Baddeley & Della Salla, 1996
; Schneider & Jarvik, 1984
). Furthermore, experienced smokers report that even IV-nicotine, which more closely mimics the pharmacokinetics of smoking than do these dosage forms, produces less relaxation, less satisfaction, and less relief from craving than smoking (Westman, Behm, & Rose, 1996
). Still, our results indicated that smoking one cigarette did not improve performance on the N
-back task by abstinent smokers.
This lack of effect could reflect an insufficient restoration of nicotine levels by one cigarette. Alternatively, a positive effect may require sustained activation of nicotinic acetylcholine receptors or production of a neuromodulatory product. Notably, a return to baseline performance on a digit recall task was observed within 4–8 h but not 1 h of reinitiating smoking following deprivation for 10 days (Snyder et al., 1989
). It is therefore possible that in contrast to the relatively well documented, immediate effect of nicotine to improve sustained and selective attention in abstinent smokers (Pritchard & Robinson, 1998
), the normalization of working memory function may require more time. The negative finding of acute smoking on the N
-back performance is, nevertheless, in conflict with observations that smoking a single cigarette restored function of the articulatory loop of working memory (Blake & Smith, 1997
), and shortened reaction times on a Sternberg task (Houlihan et al., 2001
). These contradictory results may reflect differences in the cognitive tests used, and the fact that working memory consists of various subcomponents, such as storage and manipulation of information and rehearsal of performance (Baddeley, 1996
). The substrates of these subcomponents have been distinguished from one another neuroanatomically (Awh et al., 1996
; Baker, Frith, Frackowiak, & Dolan, 1996
; Cohen et al., 1997
; McCarthy et al., 1996
) and thus may also respond differently to smoking manipulations. It is also possible, particularly given that the effect of the smoking manipulation could only be assessed via an interaction with condition, that the lack of effect was a Type II error.
The present results were mixed with respect to the hypothesized relationship between subjective craving and the effects of smoking manipulations on working memory. Within-session smoking did not produce a statistically significant effect on performance, but it effectively reduced subjective craving and withdrawal symptoms. These observations suggest dissociation between the neural substrates underlying withdrawal-based working memory deficits and the factors underlying subjective craving. Between-session comparisons produced a decrease in craving and withdrawal by individual smokers in abstinence relative to satiety and corresponding decreases in latency, error rate, and CO levels. Although larger sample sizes are required for definitive statements, these data taken together suggest that overlapping but not identical factors contribute to cigarette craving and working memory impairments during withdrawal. To summarize, this study provides evidence for a deficit in working memory associated with acute withdrawal from smoking. Such a deficiency could contribute to the maintenance and relapse of smoking behavior.