Table II. Studies of functional connectivity in fMRI. *Studies arranged chronologically by year. ACC, anterior cingulate cortex; DLPFC, dorsolateral prefrontal cortex; fMRI, functional magnetic resonance imaging; IGD, internet gaming disorder; OFC, orbitofrontal cortex; VMHC, voxel-mirrored homotopic connectivity; VTA/SN, ventral tegmental area/substantia nigra. Parts of Tables I and II reproduced with permission from ref 6: Weinstein A, Livny A, Weizman A. New devel­opments in brain research of internet and gaming disorder. Neurosci Biobehav Rev. 2017;75:314-330. Copyright © Elsevier 2017.

Citation*	Method	Participants	Main findings
Wee et al,27 2014	Functional connectivity in fMRI	17 IGD adolescents 16 control participants	Disruption of functional connectivity in the frontal, occipital, and parietal lobes. Functional connectivity with the frontal, occipital, and parietal lobes correlated with IGD severity.
Chen et al,37 2014	Functional connectivity in fMRI	29 IGD smokers 22 IGD nonsmokers 30 control participants	Decreased resting-state functional connectivity with posterior cingulate cortex in the right gyrus rectus. Increased resting-state functional connectivity in the left middle frontal gyrus in smokers with IGD compared with nonsmokers with IGD.
Dong et al,26 2015	Functional connectivity in fMRI	35 IGD 36 control participants	Lower functional connectivity in executive-control network. Functional-connectivity measures in executive-control networks were negatively correlated with Stroop effect and positively correlated with brain activations in executive-control regions across groups.
Ko et al,35 2015	Gray-matter density and functional connectivity in fMRI	30 male IGD 30 control participants	Lower gray-matter density in the bilateral amygdala and higher impulsivity. Lower functional connectivity with the left amygdala over the left DLPFC and with the right amygdala over the left DLPFC and OFC. Higher functional connectivity with the bilateral amygdala over the contralateral insula. Functional connectivity between the left amygdala and DLPFC negatively correlated with impulsivity. Functional connectivity of the right amygdala to the left DLPFC and OFC also negatively correlated with impulsivity.
Hong et al,38 2015	Functional connectivity in fMRI in subdivisions of striatum	12 male IGD adolescents 11 male control participants	Reduced dorsal putamen functional connectivity with the posterior insula-parietal operculum. Time spent playing online games predicted significantly greater functional connectivity between the dorsal putamen and bilateral primary somatosensory cortices. Lower functional connectivity between the dorsal putamen and bilateral sensorimotor cortices in healthy control participants.
Wang et al,39 2015	Functional connectivity and voxel-mirrored homotopic connectivity (VMHC) method	17 IGD 24 healthy control participants	Decreased VMHC between the left and right superior frontal gyrus (orbital part), inferior frontal gyrus (orbital part), middle frontal gyrus, and superior frontal gyrus.
Zhang et al,30 2016	Functional connectivity of the insula in fMRI	74 IGD young adults 41 control participants	Enhanced functional connectivity between the anterior insula and a network of regions including ACC, putamen, angular gyrus, and precuneous. Stronger functional connectivity between the posterior insula and post-central gyrus, precentral gyrus, supplementary motor area, superior temporal gyrus. IGD severity was positively associated with connectivity between the anterior insula and angular gyrus, and superior temporal gyrus, and with connectivity between the posterior insula and superior temporal gyrus. Duration of internet gaming was positively associated with connectivity between the anterior insula and ACC.
Cai et al,40 2016	Functional connectivity in fMRI in striatal nuclei (caudate, putamen, and nucleus accumbens) volumes	27 IGD adolescents 30 control participants	Increased volumes of dorsal striatum (caudate) and ventral striatum (nucleus accumbens) and more errors on the Stroop task. Caudate volume correlated with Stroop task performance, and nucleus accumbens volume was associated with the internet addiction test score in the IGD group.
Du et al,34 2017	Resting-state functional connectivity density in fMRI	27 male IGD adolescents 35 healthy control participants	IGD adolescents exhibited higher global/long-range resting-state functional connectivity in the bilateral dorsal lateral prefrontal cortex (DLPFC) and the right inferior temporal cortex/fusiform than healthy control participants.
Jin et al,29 2016	Functional connectivity	25 IGD adolescents 21 age- and gender-matched control participants	Decreased functional connectivity between the insula, and temporal and occipital cortices and dorsal striatum, pallidum, and thalamus in IGD. Some of those changes were associated with the severity of IGD.
Wang et al,25 2016	Functional connectivity	37 IGD 35 matched control participants	Reduced connectivity in the prefrontal cortex, left posterior cingulate cortex, right amygdala, and bilateral lingual gyrus, and increased functional connectivity in sensory-motor–related brain networks in IGD.
Park et al,36 2017	Functional connectivity in fMRI	19 IGD adolescents 20 age-matched control participants	Higher impulsiveness, higher global efficiency, and lower local efficiency pathological states. Topological alterations were specifically attributable to inter-regional connections incident on the frontal region, and the degree of impulsiveness was associated with the topological alterations over the frontal-limbic connections.
Yuan et al,15 2016	Functional connectivity in fMRI	28 IGD adolescents 25 control participants	Reduced fractional anisotropy in salience network, right central executive network tracts, and between-network (the ACC-right DLPFC tracts). Correlation between the effective and structural connection from salience network to central executive network and the number of errors during incongruent condition in Stroop task in both IGD and control participants.
Kang et al,32 2018	Resting-state functional connectivity	15 IGD adolescents with insecure attachment 15 healthy control adolescents with secure attachment	Functional connectivity from the left amygdala to the left parahippocampal gyrus, left medial frontal gyrus, and left inferior frontal gyrus, and from the right amygdala to the left caudate, right claustrum, and left inferior frontal gyrus increased. In IGD adolescents, functional connectivity from the left amygdala to the left frontal orbital gyrus, and from the right amygdala to the right corpus callosum also increased.
Han et al,33 2018	Resting-state functional connectivity	30 IGD 30 control participants	IGD showed lower static functional connectivity between the right DLPFC and the left rolandic operculum and higher static functional connectivity between the right DLPFC and the left pars triangularis. IGD had decreased dynamic functional connectivity between the right DLPFC and the left insula, right putamen and left precentral gyrus, and increased dynamic functional connectivity in the left precuneus. The dynamic functional connectivity between the right DLPFC and the left insula was negatively correlated with the severity of IGD.
Wang et al,31 2019	Resting-state functional connectivity and diffusion tensor imaging–based structural connectivity of VTA/SN circuits	33 male IGD 28 male control participants	The nucleus accumbens and medial OFC showed lower resting-state functional connectivity with VTA in IGD participants. Resting-state functional connectivity strength of VTA–right nucleus accumbens and VTA-left medial OFC correlated negatively with internet addiction test score in IGD participants. IGD participants showed lower structural connectivity in bilateral VTA-nucleus accumbens tracts, but the connectivity did not correlate with internet addiction test score.