Effect of smoking on the subcortical structure of the brain

Abstract

Background: Previous studies regarding effect of cigarette smoking and nicotine dependency on the subcortical brain has concentrated healthy, middle-aged adults with heavy smoking habits and has each concentrated on a single subcortical region to measure its role in a specific cognitive function. This study focuses to search for the effect cigarette smoking and degree of nicotine dependency has on the overall subcortical morphology in both the young general smokers and the young light smokers. Methods: Healthy, young (24 $\pm$ 3 years of age) smokers (n = 20) and non-smokers (n = 21) were compared in 15 subcortical structures in volume and shape using images derived from 3 Tesla MRI. Additional comparison was conducted between light smokers (n = 19) and pure non-smokers (n = 20) whom were all selected from the original subjects. The association between left nucleus accumbens, right caudate nucleus subfields, right hippocampus subfields and clinical measures regarding smoking habits and degree of nicotine dependency was further examined. Results: Smokers showed significant dentures in shape on the right head, right dorsal lateral body, and right tail of caudate nucleus compared to the non-smokers, while light smokers showed significant rise in shape of the left nucleus accumbens compared to the pure non-smokers. The volume of the lateral head to body region of the right caudate nucleus was negatively associated with pack-year. Multiple clinical measurements for smoking history and nicotine dependency showed positive association with right hippocampal fissure volume. Pack-year had negative association with right hippocampal tail and right hippocampal-amygdaloid transition region (HATA) volume. Pack-year also showed negative associative tendency with right whole hippocampal volume. Conclusions: Light smokers are first more sensitive to change at the left nucleus accumbens. Change at the right caudate nucleus and right hippocampal shape and volume becomes more prominent as smoking habits worsen, although the change was not directly affected by smoking habits and nicotine dependency. It seems that the overall not significant yet subtle changes by cigarette smoking in the volumes of these subcortical areas cause the visible changes in shape. How change in left nucleus accumbens shape does not show correlation with any clinical measurements suggests that it is not the severity or longevity of nicotine dependence that causes the change but that nicotine exposure alone is suffice for the change. The different results derived from the two different group comparisons highlight the difference in nature of the different smoking habits and their subsequently different impacts on the brain. The subcortical areas that showed significant group difference and/or correlation with the clinical measures may be prime targets to be searched as signs of nicotine dependency development.