Table 1.

Summary of structural MRI studies.

Authors (Year)	Sample	Mean Age	PSNSU	SNS Assessment Tool	Design	Main Results	Quality Assessment
Achterberg et al. (2022) [56]	189 individuals categorised into high (n = 52, females = 68%) vs. low (n = 137, females = 45%) SNS use groups.	10–25	Yes	Modified Compulsive Internet Use Scale [58].	Longitudinal design (3 annual scans). Assessed cortical thickness and surface area of ROIs.	The high (vs. low) group had thicker lateral and medial PFC at baseline. The high group showed a faster reduction in LPFC and TPJ over 3 years (non-FDR corrected).	High
He, Turel and Bechara (2017) [49] a	20 Facebook users (females = 10).	20.3	Yes	Modified Compulsive Internet Use Scale [58].	GMV was used to predict the severity of SNS addiction.	SNS addiction was associated with reduced GMV in the amygdala but increased GMV in the ACC/MCC.	Moderate
He et al. (2017) [47]	50 Facebook users categorised into excessive (n = 25) vs. non-excessive (n = 25) use groups, with 8 females in each group.	27	Yes	Modified Compulsive Internet Use Scale [58].	GMV was correlated with excessive SNS use scores and differences between groups were compared.	Excessive use group had reduced GMV in the bilateral amygdala and right ventral striatum. GMV of these regions were negatively correlated with excessive use scores.	High
He et al. (2018) [57] a	Sample same as He, Turel and Bechara [49].	20.3	Yes	Modified Compulsive Internet Use Scale [58].	DTI was used and ROI analysis was performed using subregions of the corpus callosum. Supplementary whole-brain voxel-wise analysis (using Tract Based Spatial Statistics; TBSS) also performed.	Excessive SNS use associated with reduced white matter connectivity in the body and splenium of the corpus callosum (non-FDR corrected). TBSS analysis revealed reduced connectivity in the forceps minor and ventral semantic pathway.	Moderate
Lee et al. (2019) [35] b	88 smartphone users categorised as healthy controls (n = 49, females = 17) vs. problematic users (n = 39, females = 10).	22.6	Yes	Korean Smartphone Addiction Proneness Scale [59].	ROI analysis performed on fronto-cingulate region. Differences in GMV and correlations with addiction severity analysed. Subsequent whole-brain analysis performed.	ROI analysis revealed smaller right OFC GMV in problematic users. Reduced GMV in the OFC correlated with higher addiction scores.	High
Montag et al. (2017) [46]	62 Facebook users (females = 25).	23.2	Yes	Online Social Network Addiction Scale [60].	Mobile app tracked participants Facebook usage across 5-weeks. Facebook use and SNS addiction were correlated with GMV in the NAc.	Left and right NAc GMV was negatively correlated with Facebook use. Reduced GMV in the right NAc was associated with more addicted Facebook use.	High
Montag et al. (2018) [48]	61 WeChat users (females = 21).	22.3	Yes	Modified short Young’s Internet Addiction Test [61].	WeChat use intensity and addiction severity were correlated with GMV.	WeChat addiction was negatively correlated with subgenual ACC GMV. Reduced GMV in the NAc was associated with higher usage of WeChat’s paying function (but not WeChat addiction).	High
Turel et al. (2018a) [53]	33 Facebook users (females = 21).	23.1	No	N/A	Using a whole-brain analysis, correlations between GMV and Facebook use were assessed whilst controlling for age and sex.	Three clusters of GMV: bilateral posterior superior temporal gyrus/middle temporal gyrus (pSTG/MTG), and left posterior fusiform gyrus, were positively correlated with Facebook use.	High
Turel et al. (2018b) [54]	32 Facebook users (females = 6).	31.2	Yes	Modified Online Video Game Addiction Scale [62].	Computer-based delay discounting task completed before MRI. Using a whole-brain and ROI analysis, GMV was correlated with SNS addiction and delayed discounting whilst controlling for age and sex.	ROI analysis revealed negative correlations between GMV in left and right posterior insula (PI) and delayed discounting as well as addiction. Delayed discounting mediated the relationship between SNS addiction and reduced GMV in left/right PI.	High

Note. PSNSU refers to studies that investigated the neural correlates of problematic/compulsive SNS use. ^a He, Turel and Bechara [49] and He et al. [57] used the same sample of Facebook users (n = 20) as a task-based fMRI study by Turel et al. [63]. ^b Lee et al. [35] used the same sample of smartphone users (n = 88) as a resting-state fMRI study by Lee et al. [36]. Although SNS use was not assessed directly, participants who used smartphones primarily for other purposes (e.g., gaming) were excluded.