The BOLD signal has been confirmed to indirectly reflect neural activity, and the low-frequency fluctuations in the resting state, although not conclusively proven, have been attributed to neural spontaneous activity (Fox and Raichle, 2007). Recent studies using diffusion tensor imaging (Greicius et al., 2009) and task-based meta-analyses (Toro et al., 2008) suggest that resting-state functional connectivity reflects structural connectivity and that networks identified in the resting-state mimic those identifiable with a lot of task paradigms. Meanwhile, resting-state functional connectivity was found among some brain regions implicated in addiction in recent studies in normal participants (Di Martino et al., 2008; Margulies et al., 2007; Roy et al., 2009). As dysfunctions in these regions were robustly proven in drug addiction (with human and animal models) (Kalivas and O'Brien, 2008; Volkow et al., 2007), we suggest that the altered functional connectivity found in HU in the present study may be a neurobiological indicator of addiction related abnormal functional organization in neural networks related to reward, craving and motivation processing which leads to addiction related compulsive drug-seeking behaviors.
