Brain activity in cigarette smokers performing a working memory task: Effect of smoking abstinence

Background: When nicotine-dependent human subjects abstain from cigarette smoking, they exhibit deficits in working memory. An understanding of the neural substrates of such impairments may help to understand how nicotine affects cognition. Our aim, therefore, was to identify abnormalities in the circuitry that mediates working memory in nicotine-dependent subjects after they initiate abstinence from smoking. Methods: We used blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to study eight smokers while they performed a letter version of the N-Back working memory task under satiety (<= 1.5 hours abstinence) and abstinence (>= 14 hours abstinence) conditions. Results: Task-related activity in the left dorsal lateral prefrontal cortex (DLPFC) showed a significant interaction between test session (Satiety, abstinence) and task load (1-back, 2-back, and 3-back). This interaction reflected the fact that task-related activity in the satiety condition was relatively low during performance of the 1-back task but greater at the more difficult task levels, whereas task-related activity in the abstinence condition was relatively high at the 1-back level and did not increase at the more difficult task levels. Conclusions: We conclude that neural processing related to working memory in the left DLPFC is less efficient during acute abstinence from smoking than at smoking satiety.