## 4 Discussion  
The present study investigated the effect of age and symptom duration of women with fibromyalgia in EEG power spectrum frequency bands (theta, alpha, beta-1, beta-2, and beta-3). Analyzing the results, significant correlations showed that the impact of the years suffering from fibromyalgia symptoms on brain aging might be even higher than the impact of the actual age of the participants. This was  
Figure 1: Channel comparison between the two groups (shorter duration versus longer duration of symptom groups) in theta power. Error bars represent the standard error of the mean. *: Significant higher values (\(p<0.05\)) between longer duration of fibromyalgia symptoms group versus shorter duration of fibromyalgia symptoms group. Figure 2: Channel comparison between the two groups (shorter duration versus longer duration of symptom groups) in alpha power. Error bars represent the standard error of the mean. Significant between-group differences were not found. also supported by significantly higher theta power being found in the group that was suffering from fibromyalgiaglia for more years. The long-term consequences of pain have traditionally been of great interest in neuroscience [29]. In this regard, this is the first study of fibromyalgia patients reporting an association between the duration of the symptoms and an altered brain dynamic. These findings support previous research focused on chronic back pain patients where altered brain activity and gray matter decreases correlated with the duration of the pain [21; 22]. Thus, fibromyalgia symptoms might elicit similar long-term responses in the brain dynamic to those caused by pain alone, but further studies are needed to confirm this hypothesis. Previous studies have shown altered brain dynamics between fibromyalgia and pain-free controls [5; 11; 12], and there is certain evidence about the seeming alteration of theta power in fibromyalgia patients [30]. In this sense, [PERSON], [PERSON], [PERSON], and [PERSON] [5] observed alterations in EEG coherence in fibromyalgia patients, showing greater EEG coherence over the left than over the right hemisphere in the centro-parietal area in a wide range of frequency bands (2 to 30 Hz). They discussed that these findings could suggest an over-activation of the pain network together with an imbalance of intra-hemispheric EEG coherence in fibromyalgia patients as compared with pain-free controls, even when no stimulation was applied. Furthermore, alterations in the theta band were also reported in the resting state in fronto-central brain regions, which are relevant in cognitive-attentional aspects of pain processing and pain inhibition [30; 31]. In this line, the authors related these alterations to ongoing tonic pain and fatigue in fibromyalgiagia. However, according to our results, an altered theta power band may be not only associated with the ongoing pain and fatigue, but it could also be the result of years suffering from fibromyalgia symptoms. Regarding alterations in theta power, previous studies have found them in Alzheimer's disease [14; 32], mild cognitive impairment [33; 34], or even related with brain aging in healthy people [15]. The authors related these alterations with hippocampus atrophy, which is located in the frontal areas [17; 33] and also in temporopariatal areas in Alzheimer's disease patients [32], which is in line with the results from the current study. Furthermore, in fibromyalgia [35] and chronic pain [18; 36], a significant reduction in important grey matter structures such as the hippocampus has been reported to be an indicator of hippocampus atrophy in fibromyalgiagia. In the current study, correlations between power spectrum and age were not significant in any of the channels. Therefore, the effect of age in the differences obtained in those channels is limited, whereas the duration of symptoms seems to be the key variable under those alterations. In that sense, another previous study showed that fibromyalgia symptoms could be partially explained by hippocampus symptoms [37].