**5. Conclusions**

Treatment of FMS patients with a multispecies probiotic for 8 weeks resulted in a tendency towards fewer errors in attention to relevant stimuli, particularly in a task that required inhibitory control at the motor level. However, this treatment had no effect on memory, specifically on working memory. These findings, along with those of our previous research on impulsivity, point to the importance of using probiotics as a therapeutic option in FMS. Nonetheless, more research is needed given the potential role of probiotics in FMS, especially since dysbiosis has been reported in FMS patients. In future studies, authors should consider exploring the effect of a specific probiotic strain on the treatment of cognitive impairment.

**Author Contributions:** D.C., N.S.-L., F.C. and P.R. designed research, conducted research, analyzed data and performed statistical analysis; D.C. and P.R. wrote the initial manuscript; N.S.-L. and F.C. critically reviewed the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board of Universidad de Almeria (UAL/1-270415).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to ethical considerations.

**Acknowledgments:** We would like to thank the staff of the Almeria Fibromyalgia Association (AFIAL—Spain) and the El Ejido Fibromyalgia Association (AFIEL—Spain) for their assistance throughout the development of this study. In addition, we wish to thank Nutergia and Complementos Fitonutricionales for providing the probiotics and placebo free of charge.

**Conflicts of Interest:** The authors declare no conflict of interest.
