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Visual presentation of appetitive and negative cues triggers fast responses in the human brain. Here we assessed functional MRI (fMRI) responses to food, cocaine, and neutral cues presented at a subliminal ("unconscious", 33 ms) and supraliminal ("conscious", 750 and 3000 ms) level in healthy, cocaine naïve volunteers. Because there is evidence of circadian variability in reward sensitivity, our second aim was to assess diurnal variability in the brain's reactivity to cues. Sixteen participants completed two randomly ordered fMRI sessions (once 9-11 AM and another 5-7 PM). in which food, cocaine, and neutral cues were presented for 33, 750 and 3000 ms. Participants rated food cues as positive and "wanted" (more so in evenings than mornings), and cocaine cues as negative (no diurnal differences). fMRI showed occipital cortex activation for foodneutral, cocaineneutral and cocainefood; dorsolateral prefrontal cortex for cocaineneutral and cocainefood, and midbrain for cocainefood (all p

Dopamine projections from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) and from the substantia nigra (SN) to the dorsal striatum are involved in addiction. However, relatively little is known about the implication of these circuits in Internet gaming disorder (IGD). This study examined the alteration of resting-state functional connectivity (RSFC) and diffusion tensor imaging (DTI) -based structural connectivity of VTA/SN circuits in 61 young male participants (33 IGD and 28 healthy controls). Correlation analysis was carried out to investigate the relationship between the neuroimaging findings and the behavioral Internet Addiction Test (IAT). Both the NAc and medial orbitofrontal cortex (mOFC) showed lower RSFC with VTA in IGD subjects compared with controls. Moreover, the RSFC strength of VTA-right NAc and VTA-left mOFC correlated negatively with IAT in IGD subjects. The IGD subjects also showed lower structural connectivity in bilateral VTA-NAc tracts compared with controls, but the connectivity did not correlate with IAT in IGD. We provide evidence that functional and structural connectivity of the VTA-NAc pathway, and functional connectivity of the VTA-mOFC pathway are implicated in IGD. Since these pathways are important for dopamine reward signals and salience attribution, the findings suggest involvement of the brain DA reward system in the neurobiology of IGD. The association of functional but not structural connectivity of VTA circuits with IAT suggests that while lower structural connectivity might underlie vulnerability for IGD, lower functional connectivity may modulate severity. These results strengthen the evidence that IGD shares similar neuropathology with other addictions.

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