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Methods: 41 chronic ketamine users from two drug rehabilitation centers (the Kangda Voluntary Drug Rehabilitation Centers in Hunan Province and the Department of Addiction Medicine, Hunan Brain Hospital) and 44 healthy non-drug use control subjects from a combination of targeted site sampling, advertisement, and snowball sampling referrals were recruited in this study. All ketamine users met the DSM-IV criteria for lifetime ketamine dependence determined from the Structured Clinical Interview. All subjects were scanned with diffusion-weighted MRI and high-resolution whole brain volume T1-weighted MRI under a 3.0-Tesla Siemens scanner. 68 cortical regions and 8 sub-cortical regions were selected as network nodes. Whole brain deterministic tractography was performed. The number of streamlines connecting all pairs of regions was calculated and thresholded to construct a set of undirected graphs for every subject. Graph theoretical analysis was then applied to quantify the efficiency of these networks.
Results: 41 chronic ketamine users (8 females; mean age 26.9 years, SD:4.87; mean years of education 11·9 years, SD: 2.8) and 44 healthy controls (10 females; mean age 26.3 years, SD 5.84, mean years of education 15.0 years, SD 2.60) were included in the analysis. Mean age of first ketamine use was 23.10 (SD: 5.21) years old. Mean ketamine use duration was 41.2 (SD: 21.53) months. Both of the chronic ketamine users and control subjects showed a small-world organization of the white matter networks. However, the ketamine users have a reduced small-world index compared with health controls (mean: 3.36, SD: 0.08 verse mean: 3.57, SD: 0.08; t: –12.85, p < 0.001).
Conclusions: The current study provides the first evidence for small-world networks disruption in chronic ketamine users.