Ocon, Anthony J · Frontiers in physiology · 2013 · DOI
ME/CFS causes cognitive difficulties that patients often describe as "brain fog"—a feeling of foggy thinking, slow mental processing, and trouble concentrating. This review suggests brain fog may result from reduced blood flow to the brain combined with the physical stress of standing (which worsens symptoms in many patients), plus the extra mental effort required to complete tasks. Understanding these overlapping factors could help explain why cognitive symptoms feel so exhausting.
This study provides a unifying mechanistic framework for understanding how and why cognitive symptoms develop in ME/CFS, moving beyond dismissing them as mild impairment. For patients, it validates that brain fog is a real physiological phenomenon rather than psychological; for researchers, it identifies testable hypotheses linking orthostatic dysfunction and cerebral hemodynamics to cognitive dysfunction.
This review does not prove causation—it proposes correlations and mechanisms based on existing literature rather than new experimental data. The relative contributions of blood flow changes, orthostatic intolerance, and increased cortical effort to brain fog cannot be quantified from this work. It also does not establish whether cognitive symptoms are primary or secondary to other ME/CFS pathology.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Ocon, Anthony J (2013). Caught in the thickness of brain fog: exploring the cognitive symptoms of Chronic Fatigue Syndrome.. Frontiers in physiology. https://doi.org/10.3389/fphys.2013.00063
BibTeX
@article{mecfsatlas-ocon-2013-caught-thickness,
author = {Ocon, Anthony J},
title = {Caught in the thickness of brain fog: exploring the cognitive symptoms of Chronic Fatigue Syndrome.},
journal = {Frontiers in physiology},
year = {2013},
doi = {10.3389/fphys.2013.00063},
note = {PubMed: 23576989},
url = {https://www.mecfsatlas.com/evidence/ocon-2013-caught-thickness},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/ocon-2013-caught-thickness
Contribute
Private, reviewed by a human. Not a public comment thread.