Abstract
Previous researches have explored the changes of functional connectivity caused by smoking with the aid of fMRI. This study considers not only functional connectivity but also effective connectivity regarding both brain networks and brain regions by using a novel analysis framework that combines independent component analysis (ICA) and Granger causality analysis (GCA). We conducted a resting-state fMRI experiment in which twenty-one heavy smokers were scanned in two sessions of different conditions: smoking abstinence followed by smoking satiety. In our framework, group ICA was firstly adopted to obtain the spatial patterns of the default-mode network (DMN), executive-control network (ECN), and salience network (SN). Their associated time courses were analyzed using GCA, showing that the effective connectivity from SN to DMN was reduced and that from ECN/DMN to SN was enhanced after smoking replenishment. A paired t-test on ICA spatial patterns revealed functional connectivity variation in regions such as the insula, parahippocampus, precuneus, anterior cingulate cortex, supplementary motor area, and ventromedial/dorsolateral prefrontal cortex. These regions were later selected as the regions of interest (ROIs), and their effective connectivity was investigated subsequently using GCA. In smoking abstinence, the insula showed the increased effective connectivity with the other ROIs; while in smoking satiety, the parahippocampus had the enhanced inter-area effective connectivity. These results demonstrate our hypothesis that for deprived heavy smokers, smoking replenishment takes effect on both functional and effective connectivity. Moreover, our analysis framework could be applied in a range of neuroscience studies.
Highlights
Drug addiction is a complex brain disorder characterized by the compulsive consumption of a deleterious drug, the fundamental mechanisms of which are studied in the neuroscience field
For task-negative’’ network (TNN), the anterior DMN (aDMN) mainly located in the anterior cingulate cortex (ACC), and the medial and superior PFC; while the posterior DMN (pDMN) located in the posterior cingulate cortex (PCC) along with the precuneus and inferior parietal lobe
In the resting-state of smoking abstinence, enhanced functional connectivity in both the aDMN and pDMN was indicated. In these two TNNs, hemodynamic responses were increased in the dorsal/rostral ACC, supplementary motor area (SMA) and dlPFC, as well as the middle occipital gyrus and inferior frontal/temporal gyrus in the condition of smoking abstinence; while after replenishment, the RS_abs RS_sat rACC dlPFC Precuneus
Summary
Drug addiction is a complex brain disorder characterized by the compulsive consumption of a deleterious drug, the fundamental mechanisms of which are studied in the neuroscience field. A widely used task in smoking research is the visual cue-exposure task, in which smoking-related visual cues and neutral cues are presented to participants during scanning [8,9,10] This type of study is essential for delineating the acute effects of smoking on circumscribed brain areas, the existence of intrinsic and spontaneous hemodynamic activity in resting-state may reveal the inherent mechanisms of smoking on brain functions more efficaciously. Identified resting-state neural mechanism features are less likely to be confounded by subtle differences in specific task designs For these reasons, a resting-state experiment design has been widely adopted in smoking studies [11,12,13]
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