1. Resting state in addiction. Non-invasive brain imaging has contributed important insights into the neuroplastic adaptations that result from chronic drug intake, but additional experimental approaches are needed to better capture the totality of the motivational, affective, cognitive, genetic and pharmacological complexities of addiction. Recent advances in assessing network dynamics through resting-state functional connectivity (rsFC) may allow for such systems-level assessments. Circuit connectivity may inform specific neurobiological substrates underlying psychological dysfunctions associated with reward, affective and cognitive processing often observed in drug addicts. Using nicotine addiction as an exemplar, we subsequently provide a heuristic framework to guide future research by linking recent findings from intrinsic network connectivity studies with those interrogating nicotine's neuropharmacological actions. Emerging evidence supports a critical role for the insula in nicotine addiction. Likewise, the anterior insula, potentially together with the anterior cingulate cortex, appears to pivotally influence the dynamics between large-scale brain networks subserving internal (default-mode network) and external (executive control network) information processing. We suggest that a better understanding of how the insula modulates the interaction between these networks is critical for elucidating both the cognitive impairments associated with withdrawal and the performance-enhancing effects of nicotine administration. This may be usefully in designing and developing novel smoking cessation treatments. 2.Individual differences in amygdala reactivity: Hyperactive amygdala functioning may underlie emotional dysregulation during early smoking abstinence and thus represents one neurobiological target for pharmacological cessation aids. Available pharmacotherapies such as varenicline and nicotine replacement aid only a subset of individuals with smoking cessation and therefore elucidating the neurobiological impact of these medications is critical to expedite improved interventions. We looked at the effects of varenicline and nicotine on amygdala functioning in abstinent cigarette smokers. Using fMRI, we assessed task performance and amygdala reactivity during an emotional face matching paradigm following administration of varenicline and nicotine to 24 abstinent smokers and 20 nonsmokers. All participants underwent 17 days of varenicline and placebo pill administration and were scanned, on different days under each condition, wearing a transdermal nicotine or placebo patch. During the amygdala reactivity paradigm, nicotinic acetylcholine receptor (nAChR) stimulation by nicotine and varenicline decreased reaction times (RT) in abstinent smokers only. Smokers showed variability in pharmacologically-induced performance improvements and were dichotomized into high/low RT-improvement subgroups, as were nonsmokers. In the high RT-improvement smokers, elevated amygdala reactivity during smoking abstinence was downregulated by nAChR stimulation. In contrast, varenicline and nicotine did not modulate amygdala functioning in the low RT-improvement smokers or either nonsmoker subgroup, all of whom displayed moderate levels of amygdala reactivity without drug. This suggests that pharmacological cessation aids most robustly dampened amygdala functioning in those smokers appearing susceptible to abstinence-induced effects, and by inference, smoking relapse when attempting to quit. Such findings provide a step towards fractionating the smoker phenotype by quantifiable neurobiological characteristics. 3.Amygdala-insula functional circuits. Little is known about amygdala and insula circuit-level interactions with other brain regions during nicotine withdrawal or following pharmacotherapy administration. We examined the impact of varenicline and nicotine on amygdala- and insulacentric circuits using rsFC in an fMRI study in 24 abstinent smokers and 20 nonsmokers. Subjects were scanned with nicotine or placebo patch. We examined the impact of varenicline and nicotine (both alone and in combination) on amygdala and insula rsFC using seed-based assessments. rsFC strength in an amygdala-insula circuit was down-regulated by varenicline and nicotine in abstinent smokers. Using this identified insula region as a new seed, both drugs also decreased rsFC between insula and, among other regions, constituents of the canonical default-mode network (DMN: e.g., posterior cingulate cortex, ventro/dorsomedial prefrontal cortex, parahippocampus). Drug-induced rsFC modulations were critically linked with nicotine withdrawal in smokers only. These results indicate that nicotine withdrawal is associated with elevated amygdala-insula and insula-DMN functional interactions. As these potentiated interactions were down-regulated by two pharmacological cessation aids, connectivity strength in amygdala and/or insula circuitry may serve as a biomarker of nicotine withdrawal that could be leveraged in the development of improved cessation interventions. 4. Nicotine and reward: The reinforcing effects of nicotine are mediated by brain regions that also support temporal difference error (TDE) processing;yet, the impact of nicotine on TDE is undetermined. Dependent smokers (n=21) and matched controls (n=21) were trained to associate a juice reward with a visual cue in a classical conditioning paradigm. Subjects subsequently underwent fMRI sessions in which they were exposed to trials where they either received juice as temporally predicted or where the juice was withheld (negative TDE) and later received unexpectedly (positive TDE). Subjects were scanned in two identical sessions, except that smokers had a transdermal nicotine (21 mg) or placebo patch placed before scanning. There was a reduction in TDE-related function in smokers in the striatum, which did not differ as a function of patch manipulation but was predicted by years of smoking. Activation in midbrain regions was not impacted by group or drug condition. These data suggest a differential effect of smoking status on the neural substrates of reward in distinct dopaminergic pathway regions, which may be partially attributable to chronic nicotine exposure. The failure of transdermal nicotine to alter reward-related functional processes implies that acute nicotine patch administration is insufficient to modify reward processing, which has been linked to abstinence-induced anhedonia in smokers and may play a critical role in smoking relapse. 5. Enhanced assessment of severity of addiction: fMRI studies indicate that there are significant differences in the neural circuitry and functioning of substance dependent individuals. It is unknown which of these differences are predictive of substance dependence or to what extent these differences in neural function are a consequence of genes, the environment preceding drug use, and the drug use itself. Finally, we do not have a good understanding of how such differences might speak to the severity of addiction and differential treatment outcomes. Therefore, we are examining multimodal data through a support vector machine or SVM-based pattern classifier. We trained the classifier on several neuroimaging-based measures and genetics data from 54 smokers and 24 non-smokers: 1) structural neuroimaging measures cortical gray matter volume, surface area, and thickness, and subcortical gray matter volume 2) rsFC between 164 regions of interest;and 3) 1538 SNPs in addiction-related genes. The SVM classifier was built using the LIBSVM package, and augmented by an Adaptive Boosting (Adaboost) algorithm. Preliminary data suggests that an SVM-based pattern classification approach could potentially be used for enhanced assessment of severity of addiction, and in predicting response to treatment.

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Li, Sufang; Yang, Yihong; Hoffmann, Ewa et al. (2017) CYP2A6 Genetic Variation Alters Striatal-Cingulate Circuits, Network Hubs, and Executive Processing in Smokers. Biol Psychiatry 81:554-563
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