Fibro Fog in Fibromyalgia: What It Is and Its Neurobiological Basis

What is fibro fog in fibromyalgia? Neuropsychologist Noelia Férez López analyzes the neurobiological mechanisms, alterations in attentional networks, and the impact of chronic pain on the brain. An essential guide for cognitive neurorehabilitation professionals. 

Executive summary with the key points of this article:

1. What fibromyalgia is and which cognitive functions it affects.
2. What fibro fog is and how it affects the brain.
3. What the neurobiological basis of fibro fog is.

What is fibromyalgia and how does it affect the brain?

Fibromyalgia is a chronic pain syndrome characterized by widespread musculoskeletal pain, severe fatigue, sleep disturbances, and a long list of physical and emotional symptoms. It is estimated to affect approximately 2–4% of the population, with a higher prevalence among women and people with other chronic medical conditions. 

However, many people describe something that concerns them almost as much as the pain: brain fog. From a neuropsychological perspective, we know that fibromyalgia does not only affect the body; it also involves changes in the way the brain processes, organizes, and maintains information. This is what we call the cognitive profile of fibromyalgia or “fibro fog”. 

Which cognitive functions are impaired in fibromyalgia?

Although not all people with fibromyalgia experience the same difficulties, or with the same intensity, research and clinical practice reveal a series of common patterns. These include: 

1. Executive functions: These are the brain’s “management functions,” the CEO of the nervous system that plans, organizes, prioritizes, switches tasks, inhibits impulses, and makes decisions. In clinical practice, we encounter patients who say: “I start many things but don’t finish any of them”; “if plans don’t work out as expected, I freeze.” In the neuropsychological assessment of people with fibromyalgia, we find difficulties with cognitive flexibility, inhibition, and planning tasks. 
2. Sustained and selective attention: Maintaining attention over a prolonged period or filtering relevant from irrelevant information can become a genuine uphill struggle for these patients. Everyday examples include: “I start a load of laundry and, while the machine fills, I look at my phone and don’t come back to it for another hour,” and “if there’s noise, conversations, or distractions, I lose track and get a headache.” During interventions, we observe a higher number of errors, greater attentional fluctuation , and a rapid sense of mental fatigue. 
3. Working memory and recent memory: Working memory is the “mental whiteboard” where your brain holds, for a few seconds, the information you need to use at that moment. In the daily life of a person with fibromyalgia, this may mean “I go from one room to another and no longer know what I was going to do” or “if I’m given several instructions in a row, I only remember the first one.” In clinical practice, these patients often report recurrent forgetfulness, when what may actually be failing is prior attention or the ability to manage information, rather than storage capacity.
4. Processing speed: This is the speed at which our brain takes in information, understands it, and responds. In this case, we observe that the patient needs more time to do the same things they used to do, and patients give examples such as: “I used to take care of errands in one afternoon; now I need three”; “I have trouble keeping up with a fast conversation or a work meeting.” 

Comparative studies have shown that, on average, people with fibromyalgia have more difficulty performing tasks than healthy people of the same age and educational level in the areas described above (Wu et al., 2018; Bell et al., 2018). 

What is fibro fog?

The term fibro fog is used to describe a set of symptoms involving “brain fog in fibromyalgia,” including a sense of mental slowness, difficulty thinking clearly, word-finding problems, frequent forgetfulness, and a feeling of minimal cognitive overload during tasks that were previously easy. 

The relationship between fibro fog and chronic pain

Chronic pain continuously consumes many attentional resources. The nervous system maintains sustained vigilance toward pain, which acts as permanent “background noise” and forces the brain to devote part of its executive control capacity to managing that nociceptive signal. 

Several studies show that: 

• Pain intensity correlates with poorer performance on tasks involving attention, working memory, and cognitive flexibility. 
• People with chronic pain who report more fibro fog show higher levels of pain interference in daily life and poorer occupational participation. 

These findings are consistent with describing fibro fog as part of the cognitive impact of chronic pain (Dass et al., 2023). 

Attentional and executive networks overloaded in fibro fog

Thanks to neuroimaging studies, we now know that in fibromyalgia, not only do the areas that process pain change, but so do the networks that manage attention and executive functions. In other words, there are changes in brain connectivity involved in cognitive control and in pain perception itself:

1. Frontoparietal network: Involved in planning, directed attention, decision-making, and cognitive control. In fibromyalgia, patients show a need to exert more cognitive effort for simple tasks, and communication between its nodes is less efficient. In addition, when pain is severe, the network is relegated behind other networks, such as those involved in pain perception or internal sensations.
2. Dorsal attention network: It helps us voluntarily maintain focus on a specific task. In fibromyalgia, alterations have been described, particularly when we try to perform several tasks at once or when these tasks compete with noisy environments or other stimuli. The clinical result is that feeling of “being unable to follow the thread,” even when the task is not complex.
3. Salience network: Responsible for detecting which stimuli are important and deciding what we should attend to. In fibromyalgia, this network tends to be “hijacked” by painful sensations and bodily discomfort. In other words, it constantly prioritizes pain and discomfort over other external stimuli. This causes attention to shift repeatedly toward the body and leaves fewer resources available for concentrating on other tasks such as reading, working, or having a conversation.
4. Default mode network (DMN): This is the network activated when we are at rest, thinking about our lives, remembering, or imagining the future. In fibromyalgia, greater connectivity between the default mode network and regions related to pain and interoception has been observed. This means that even during periods of “rest,” the mind may remain focused on bodily sensations and concerns associated with pain. In addition, coordination between the DMN and executive networks is less flexible, making it harder to shift from that “internal mode” (dwelling on what I feel) to a “task mode” (focusing on what I am doing) without carrying the mental fog along (Čeko et al., 2020; Napadow & Harris, 2014).

The role of sleep in fibromyalgia

Nonrestorative sleep is one of the components of fibromyalgia. Many scientific studies demonstrate lower sleep efficiency, more awakenings, and a greater proportion of light sleep in these patients (Wu et al., 2017). 

If sleep is light, fragmented, or insufficient night after night, the brain does not have time to carry out its “internal repair” and, the next day, the mind starts with reduced attentional capacity, greater difficulty learning and retaining new information, and increased irritability and pain sensitivity. 

The patient does not start the day from zero, but already in the red. They wake up tired, with a more reactive nervous system, and fibro fog appears from the very first hour: the mind is slower, more confused, and has less room to manage the demands of the day. 

Fatigue in fibromyalgia

The autonomic nervous system regulates automatic functions such as heart rate, breathing, blood pressure, and digestion. Many people with fibromyalgia have been found to show autonomic dysfunction (Kang et al., 2016), which usually manifests as: 

• Sympathetic nervous system predominance (“alert, fight-or-flight” mode). 
• Reduced parasympathetic nervous system predominance (“rest, digestion, and repair” mode). 

This means that the body spends more time in physiological tension and has greater difficulty relaxing after stress or recovering from exertion. This nervous system is more likely to sleep poorly, experience more pain, and notice greater physical and mental fatigue. 

Neurobiological basis of fibro fog

Fibro fog is not merely a subjective sensation. These complaints are underpinned by identifiable changes in the brain and nervous system: in how pain is processed, how attentional and executive networks are organized, and how the stress, sleep, and inflammatory systems respond (Napadow & Harris, 2014). 

This section reviews the main neurobiological bases that have been associated with fibro fog:

1. Central sensitization: the central nervous system becomes more excitable and responds excessively to pain signals. This hyperexcitable state affects not only how pain is perceived, but also attention. The person develops a hypervigilant attentional pattern strongly oriented toward bodily signals, triggering two responses:
   • The salience network constantly detects pain and internal discomfort, marking them as priorities.
   • The resources of the dorsal attention network are unavailable for maintaining focus on external tasks such as reading, working, or following a conversation.
   • The final result is a clear attentional bias toward the body and painful sensations.
2. Inflammation and neuroimmunology: in recent years, the idea that fibromyalgia may involve low-grade inflammation, with changes in cytokines and other immune mediators, has gained strength. These signals are also present in other conditions such as arthritis, lupus, inflammatory depression, and long COVID, and may increase pain sensitivity, promote fatigue, and affect cognitive functions (García-Domínguez, 2025).

3. Autonomic dysfunction: another neurobiological basis of fibro fog is dysfunction of the autonomic nervous system and the stress axis (hypothalamic–pituitary–adrenal axis). Our patients live in a state of hyperactivation that causes reduced heart rate variability and sympathetic predominance, resulting in a chronically activated “alarm” characterized by a mixture of pain, internal tension, palpitations, rapid breathing, or diffuse discomfort.
4. Executive dysfunction: neuroimaging studies have shown structural and functional changes in regions such as the dorsolateral prefrontal cortex (key to planning, working memory, and decision-making), the anterior cingulate cortex (involved in conflict monitoring, error management, and emotion integration), and alterations in frontostriatal circuits (through which dopamine and norepinephrine circulate). 

Conclusion

References

• Beck, A. T., Steer, R. A., & Brown, G. K. (1996). Manual for the Beck Depression Inventory–II. Psychological Corporation.
• Bell, T., Trost, Z., Buelow, M. T., Clay, O., Younger, J., Moore, D., & Crowe, M. (2018). Meta-analysis of cognitive performance in fibromyalgia. Journal of Clinical and Experimental Neuropsychology, 40(7), 698–714. 
• Broadbent, D. E., Cooper, P. F., FitzGerald, P., & Parkes, K. R. (1982). The Cognitive Failures Questionnaire (CFQ) and its correlates. British Journal of Clinical Psychology, 21(1), 1–16.
• Buysse, D. J., Reynolds, C. F., Monk, T. H., Berman, S. R., & Kupfer, D. J. (1989). The Pittsburgh Sleep Quality Index: A new instrument for psychiatric practice and research. Psychiatry Research, 28(2), 193–213.
• Čeko, M., Frangos, E., Gracely, J., Richards, E., Wang, B., Schweinhardt, P., & Bushnell, M. C. (2020). Default mode network changes in fibromyalgia patients are largely dependent on current clinical pain. NeuroImage, 216, 116877. 
• Cleeland, C. S., & Ryan, K. M. (1994). Pain assessment: Global use of the Brief Pain Inventory. Annals of the Academy of Medicine, Singapore, 23(2), 129–138.
• Dass, R., Kalia, M., Harris, J., & Packham, T. (2023). Understanding the experience and impacts of brain fog in chronic pain: A scoping review. Canadian Journal of Pain, 7(1), 2217865. 
• García-Domínguez, M. (2025). Fibromyalgia and inflammation: Unrevealing the connection. Cells, 14(4), 271.
• Häuser, W., Thieme, K., & Turk, D. C. (2010). Guidelines on the management of fibromyalgia syndrome—A systematic review. European Journal of Pain, 14(1), 5–10. 
• Fernández-Palacios, F. G., Pacho-Hernández, J. C., Fernández-de-las-Peñas, C., Gómez-Calero, C., & Cigarán-Méndez, M. (2024). Evaluation of cognitive performance in patients with fibromyalgia syndrome: A case–control study. Life, 14(5), 649. 
• Kang, J. H., Kim, J. K., Hong, S. H., Lee, C. H., & Choi, B. Y. (2016). Heart rate variability for quantification of autonomic dysfunction in fibromyalgia. Annals of Rehabilitation Medicine, 40(2), 301–309. https://doi.org/10.5535/arm.2016.40.2.301 
• Monterde, S., Salvat, I., Montull, S., & Fernández-Ballart, J. (2004). Validación de la versión española del Fibromyalgia Impact Questionnaire. Revista Española de Reumatología, 31(9), 507–513. 
• Napadow, V., & Harris, R. E. (2014). What has functional connectivity and chemical neuroimaging in fibromyalgia taught us about the mechanisms and management of “centralized” pain? Arthritis Research & Therapy, 16(5), 425. 
• Salgueiro, M., García-Leiva, J. M., Ballesteros, J., Hidalgo, J., Molina, R., & Calandre, E. P. (2013). Validation of a Spanish version of the Revised Fibromyalgia Impact Questionnaire (FIQR). Health and Quality of Life Outcomes, 11, 132. 
• Serrat, M., Almirall, M., Musté, M., Sanabria-Mazo, J. P., Feliu-Soler, A., Méndez-Ulrich, J. L., Luciano, J. V., & Sanz, A. (2020). Effectiveness of a multicomponent treatment for fibromyalgia based on pain neuroscience education, exercise therapy, psychological support, and nature exposure (NAT-FM): A pragmatic randomized controlled trial. Journal of Clinical Medicine, 9(10), 3348. 
• Wolfe, F., Clauw, D. J., Fitzcharles, M.-A., Goldenberg, D. L., Katz, R. S., Mease, P., Russell, A. S., Russell, I. J., Winfield, J. B., & Yunus, M. B. (2010). The American College of Rheumatology preliminary diagnostic criteria for fibromyalgia and measurement of symptom severity. Arthritis Care & Research, 62(5), 600–610.
• Wu, Y.-L., Chang, L.-Y., Lee, H.-C., Fang, S.-C., & Tsai, P.-S. (2017). Sleep disturbances in fibromyalgia: A meta-analysis of case-control studies. Journal of Psychosomatic Research, 96, 89–97. 
• Wu, Y.-L., Huang, C.-J., Fang, S.-C., Ko, L.-H., & Tsai, P.-S. (2018). Cognitive impairment in fibromyalgia: A meta-analysis of case-control studies. Psychosomatic Medicine, 80(5), 432–438. 
• Zigmond, A. S., & Snaith, R. P. (1983). The Hospital Anxiety and Depression Scale. Acta Psychiatrica Scandinavica, 67(6), 361–370.

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