## 2 Materials and Methods  
Main scientific databases (PubMed, Cochrane Library, and Web of Science) and Brain-Map were screened using keywords, such as [\"mild traumatic brain injury\" OR \"mTBI\" OR \"concussion\"] AND [\"voxel-based\" OR \"morphometry\" OR \"VBM\" OR \"volumetric changes\"]. PRISMA guidelines were used to conduct the screening and selection processes. The inclusion criteria were: (1) English-language studies providing full-text versions; (2) that compare GM and WM changes in mTBI adult patients and healthy controls; (3) having their results reported in the Montreal Neurological Institute (MNI) or Talairach space. The exclusion criteria formulated for the current study were: (1) duplicates; (2) studies written in other languages or not available as full-text versions; (3) not providing detailed coordinates for volumetric changes; (4) not comparing with healthy individuals (sex and age matched-controls); or (5) not providing information on the demographic description of the population samples. Data screening and selection was performed by two different investigators. For each study, the number of participants, demographic description, symptomatology, and peak coordinates were extracted.  
The meta-analysis was carried out using the SDM software package (Seed-based d Mapping software, version 6.21 for 64-bit Windows PC) [13; 14; 15] and compared the differences of regional volume changes between the two groups. For each study included in our analysis, we prepared a file with the coordinates, effect size, and sample size, following the guidelines provided by the developers [13; 14; 15], with full width at half-maximum set at 20 mm and a statistical significance threshold of \(p\) < 0.005 [16]. These values have been suggested in previous studies as exhibiting the best balance between sensitivity and specificity and the best control for false-positive rates [17].  
The statistical analysis was entirely carried out by the software including data extraction and effect-size mapping of the regional differences recreation. The mean map was then produced through a meta-analytical random-effects model with the weight of each study being calculated by the sample size, intra-study variability, and between-study heterogeneity (according to the formulas presented in the developer's software manual and the theoretical description of the methods [18]).  
The statistical significance was established with standard randomization tests. Default kernel size and statistical thresholds were used to optimize the recreation of the effect-size maps and, at the same time, to preserve robustness, as described by the method developers [19].  
In addition to the above, we conducted Jack-knife sensitivity analyses to assess the robustness of the findings by repeating the mean analysis excluding one study each time and recalculating the SMD. We carried out a heterogeneity analysis to determine significant unexplained between-study variability within the results using a random effects model with Q statistics [20; 21], and the publication bias was calculated with visual inspection of the funnel plots and using [PERSON]'s test within the SDM software, Cochrane Risk of Bias Tool, and the Robvis tool [21].