*2.2. Eligibility Criteria*

The following study inclusion criteria were applied: (1) written in English or Spanish; (2) original, peer-reviewed study; (3) adult patients (≥18 years old); and (4) focused on chronic pain and the emotional Stroop task.

The exclusion criteria were as follows: (1) written in languages other than English or Spanish; (2) review article or meta-analysis; (3) inclusion of non-adult patients (≤18 years old); and (4) commentary, report, letter, editorial, meeting, and/or congress abstract or case report.

#### *2.3. Data Extraction and Quality Assessment*

L.A.-D., C.I.M.-A., and L.R.F.-J. independently extracted study characteristics, methodologies and results, and assessed the limitations of each study. Discrepancies were reviewed by C.M.G.-S. The sequence for data extraction was as follows: first author, study name, country, year of publication, study design, sample size, number of participants in each study group, and age and sex of the participants. The characteristics of the study are shown in Table 1. C.M.G.-S. reviewed all data to ensure the accuracy of the data extraction.


**Table 1.**

Characteristics

 of selected studies on Chronic Pain and Emotional Stroop.





WL = Waitlist.

#### *2.4. Data Synthesis*

Our review focuses on studies of patients over 18 years of age, suffering from any chronic pain condition (FMS, CLBP, CNP, migraine, or TMD). In addition, all of the studies used the emotional Stroop task (or any variant thereof), and the performance of patients with chronic pain was compared (in most cases) with a control group composed by healthy participants. Attention was also paid to the activation of brain areas responsible for emotional and pain processing during the application of the emotional Stroop task, as well as to possible attentional biases towards certain types of stimuli presented in the task.

According to the objectives of this review, the type of the Stroop task performed in each study (and whether the sample had a control group) and the study design (e.g., randomized controlled trial, experimental, or case-control study) were determined. In addition, the target population, as well as the proportion of male and female participants, and their mean and standard deviation age, were ascertained. Furthermore, the main results of each study, which are shown in Table 1 (first author, study name and country, objective, diagnostic technique, sample size and age, type of emotional Stroop task, and results), were analyzed. Finally, the limitations of each study were assessed.
