ABSTRACT
Addiction is a complex disease process, encompassing a relapsing cycle of intoxication, bingeing, withdrawal and craving. While neuroimaging studies describing brain functioning at the level of single brain regions have decisively shaped our understanding of each of these stages, the importance of moving beyond this approach and investigating how brain regions assemble into brain networks, which support complex psychological processes such as reward seeking or inhibitory self-control, has long been recognized (Goldstein and Volkow 2002; Koob and Volkow 2010; Goldstein and Volkow 2011). In recent years, numerous studies have therefore started to explore the role of disrupted brain networks in addiction by investigating structural and functional connectivity between and within these large-scale brain networks. Neuroimaging can be used to evaluate structural brain connectivity through ‘diffusion-weighted imaging’, which can assess the integrity of the white matter tracts (comprised of nerve cell projections) connecting brain regions to one another. Second, functional neuroimaging can be employed to compute the strength of ‘functional connectivity’, which uses co-activation of brain regions as an indicator of shared neuronal activity between them (Shmuel and Leopold 2008). The latter is usually acquired during resting-state, a baseline state in which the brain is not actively involved in a task and drugs have not been administered. Resting-state functional connectivity therefore captures a default brain state independent of external input/challenges, providing insight into the intrinsic ‘functional architecture’ of the brain that underlies functioning during task demands (Fox and Raichle 2007). Both structural and resting-state neuroimaging are therefore useful tools for understanding the fundamental makeup of the brain and assessing how this is changed in addiction.
