## 4 Discussion
### Limb Laterality Discrimination and Pain in Fibromyalgia Pain Syndrome  
To the best of our knowledge, only one previous study has evaluated laterality discrimination in patients with FMS, although in this study, the authors found that patients with FMS had impaired ability to discriminate laterality. They also found impaired ability to discriminate two-point discrimination but did not measure the somatosensory variables which were applied in this study [22]. In the present investigation, the study of aspects related to pain and laterality discrimination in patients with FMS was deepened. Regarding somatosensory variables, our results are consistent with the results of other investigations in which PTT [8; 35] and CPM [13; 25] were measured in patients with FMS, showing alterations in pain processing and pain modulation in this population. Our results are in line with those obtained in this other research group [22] and expand current knowledge by including the judgment of laterality of the feet, performing the test with 20 or 50 images and delving into the study of pain by including measurements of PTT, CPM and strange sensations during the laterality discrimination. Our results suggest that the laterality discrimination task in patients with FMS not only presents difficulties for images of the hands but also of the feet, as is reflected both in the number of correct answers and the reaction times. At first, because the results were very similar, it seemed that there was no difference between identifying 20 or 50 images of hands or feet and the relationship between the LRJT and the PTT and CPM measurements. However, in a more in-depth statistical analysis, we found that there was a strong correlation between the ACC of 50 images of the hands and the CPM and a positive association between the ACC of 50 images of the feet and the CPM. These findings are novel for patients with FMS and open the possibility that the LRJT is a task with potential utility in the field of pain assessments in the FMS population. On the other hand, in our study, we found no correlation between the LRJT and mechanical hyperalgesia, as measured with PPT. The qualitative data collected regarding sensations \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Measures** & **PPT** & **PPT Post** & **CPM** & **FIQ** & **Pain Intensity** \\ \hline RT hands & & & & & \\ (20 images) & & & & & \\ RT hands & & & & & \\ (50 images) & & & & & \\ ACC feets & & & & & \\ (20 images) & & & & & \\ ACC feets & & & & & \\ (50 images) & & & & & \\ (50 images) & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._evoked during the LRJT were consistent with the nature of the task, since these patients did not suffer any type of pain symptomatology or unusual sensations, as the mental rotation movement occurred implicitly. In addition, seven patients with FMS reported feeling an increase in body temperature. The results of this study are also in line with those of another study in which [PERSON] et al. evaluated the ability to recognize laterality, but in patients with carpal tunnel syndrome [36]. Those authors found impaired accuracy in judging the right and left sides of hand images and proposed that the performance of these tasks occurs in brain areas similar to the imagined or realized movements [37; 38]. In contrast, in a population of patients with chronic whiplash-associated disorders, they did not find that the accuracy of imagery judgements was different from controls in terms of reaction time, but they did find a correlation between mechanical hyperalgesia and laterality judgements of the cervical spine and feet [39]. In another study of patients with lower back pain, no differences were found in the accuracy of judgement of laterality and reaction time compared to healthy controls [30]. One possible explanation for these findings is that CPM is a pain assessment tool that highlights the malfunction of descending inhibitory pain systems, which have been seen in previous research to be altered in patients with FMS [11; 12; 13].