Overall, a very carefully compiled article that is of particular importance for the study of the fractal dimension in healthy and mentally ill people. Until now, there has been no systematic review of previously published articles on these groups.

The article is essentially based on the Prisma criteria.
Nevertheless, there are some important points I would ask for a revision:

Methods and Results
- Prisma checklist: a revision of the methods section seems useful, especially statements on bias and synthesis method should be added
- please also align the results in more detail with the checklist

Discussion
- Please explain the advantages and disadvantages of the FD, e.g. in comparison to the gyrification index (GI), and relate the results to the GI, especially since there is much more work on the GI
- In addition, the neurodevelopment and neurodegeneration aspect should be discussed in more detail.

Minor points:
- Check spelling errors (e.g., page 18 "analyzed")
- Cite all articles discussed (e.g., page 21 for mild cognitive impairment and Huntington's disease)
- Pg. 10 figure and table mixed up?