The goal of this observational study is to test for behavioural and neurophysiological biomarkers in fibromyalgia patients. The main questions it aims to answer are:

• Is there a measurable decline in working memory?
• Could these measures help in fibromyalgia differential diagnosis?

Participants will:

• perform Color Comparison tasks
• perform n-back tasks

Fibromyalgia is a disease characterized by the presence of generalized musculoskeletal pain, accompanied by non-specific symptoms such as depression, sleep disturbances, anxiety, cognitive disabilities, among others. While widespread musculoskeletal pain is the predominant symptom in patients with fibromyalgia, cognitive impairments have also been widely reported, including decreased ability to concentrate, decreased short-term memory, and inability to multitask, which differentiate fibromyalgia patients from those with other chronic pain syndromes. Specifically, quantitative evidence has been found of impairment in executive functions in this group of patients, particularly in the domains of inhibitory control and working memory.

In the present study, participants (both healthy individuals and those diagnosed with fibromyalgia) will perform two cognitive tasks designed to assess the capacity and retrieval of information from working memory. The first task is the Color Comparison task, in which colored squares will appear on a computer screen for a short period of time. After a blank delay, a new set of squares will appear, and a decision has to be made about whether or not the squares are the same as the ones shown first. The task will be divided into 10 blocks of 30 trials each, with 10 trials comparing 2 colored squares, 10 trials comparing 4 colored squares, and 10 trials comparing 6 colored squares. A resting period will be given between each block. The behavioral results of this task will include reaction times and hit rates. At the same time, electroencephalographic data will be recorded to evaluate the Contralateral Delay Activity (CDA). The amplitude of this waveform is linked to the number of items allocated in working memory.

The second task that will be carried out by the participants is the n-back task. A sequence of letters will be presented, and participants will be asked to indicate whether the current stimulus matches the one presented two stimuli earlier. Sixty-two stimuli will be presented per block, and 5 blocks will be carried out. The results will be analyzed in terms of behavioral analysis and Event-Related Potentials (ERPs) analysis.

Inclusion Criteria:

Fibromyalgia patients:

• Primary diagnosis of fibromyalgia according to the criteria used by the healthcare professional in charge of the patient.
• Other comorbidities are accepted as long as the pain caused by them is less severe than the pain caused by fibromyalgia.
• Willingness and ability to fully understand the content and scope of the experiment and to comply with the experiment instructions.
• Normal or corrected-to-normal vision.

Healthy controls:

• No history of neurological diseases, chronic pain or musculoskeletal disorders.
• Willingness and ability to fully understand the content and scope of the experiment and to comply with the experiment instructions.
• Normal or corrected-to-normal vision.

Exclusion Criteria:

Fibromyalgia patients:

• Pregnancy
• History of addictive behavior, defined as alcohol, cannabis, opioids or other drugs abuse.
• Presence of fever, tuberculosis, malignant tumors, infectious processes, acute inflammatory processes.
• Lack of cooperation

Healthy controls:

• Pregnancy
• History of chronic pain or musculoskeletal or articular disorders
• History of addictive behavior, defined as alcohol, cannabis, opioids or other drugs abuse.
• Presence of fever, tuberculosis, malignant tumors, infectious processes, acute inflammatory processes.
• Lack of cooperation

The cohorts of patients and healthy controls wil be selected from the city of Paraná and surrounding areas. Through the ONG "Fibromialgia Entre Ríos Asociación Civil", the patients will be reached out and asked wether or not they are willing to participate. Additionally, flyer will be hung in major health facilities in the city and made public on social media. The cohort of healthy volunteers will be recruited after the patients for age, genre and socieconomic matching

Individual participant data (IPD) will be made available on the 'Open Science Framework' after undergoing the process of anonymization to remove any participant-identifying information. The data will consist of the raw EEG signals and raw behavioral responses to cognitive tasks. Additionally, the statistical analysis and Jupyter notebooks used to process the data will also be shared

The participant's data and the processing pipeline will be available after the data collection is finished. The supporting information (including the study protocol, the statistical analysis plan and the informed consent) will be uploaded as soon as possible.

The data will be publicly available.