https://www.sciencedirect.com/science/article/pii/S0166223625000177 Feature Review Online now February 25, 2025 Open access Defining brain fog across medical conditions Peter Denno pdenno@ic.ac.uk ∙ Sijia Zhao Masud Husain Adam Hampshire 1Department of Brain Sciences, Imperial College London, London W12 0NN, UK 2Institute of Psychiatry, Psychology, and Neuroscience, Kings College London, London WC2R 2LS, UK 3Department of Experimental Psychology, University of Oxford, Oxford OX2 6GG, UK 4Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, U Highlights The term 'brain fog' is used to convey a broad but characteristic set of symptoms, implicating cognition (particularly attention, memory, and language), affect, and fatigue. Brain fog is related to, but dissociable from, cognitive performance. Fatigue and affect influence subjective brain fog and mediate cognitive performance deficits across diagnoses. Divergent neural correlates suggest a heterogeneous aetiology. Researchers should provide clear definitions when studying brain fog, preferably replacing or complementing it with more precise terms where possible [e.g., 'post-coronavirus disease 2019 (COVID-19) neuropsychiatric symptoms' rather than 'COVID-19 brain fog']. We suggest that future research should conduct transdiagnostic comparisons of brain fog using a standardised set of measures to fractionate the distinct constructs that brain fog conflates and enable precise characterisation. Abstract 'Brain fog' is commonly reported in more than a dozen chronic diseases, but what is it? We review research across conditions which has characterised brain fog and evaluate its definitions and objective correlates. Brain fog has been used to refer to a variable set of overlapping symptoms implicating cognition, fatigue, and affect. It has been defined as a distinct symptom, a syndrome, or a nonspecific term. We consider the evidence that brain fog is a transdiagnostic entity with a common phenomenology and profile of objective cognitive deficits. We discuss where these commonalities arise and argue that linguistic ambiguity, shared cognitive impairments, and noncognitive factors are more likely than shared neurobiology. We suggest how future research might apply existing tools to disambiguate the phenomena that brain fog conflates. Keywords fatigue cognition COVID-19 chronic Illness signs and symptoms
One of those rather annoying articles in which the authors quite correctly make the point that the existing literature suffers from vagueness of definitions and un-generalisable findings, but go on to make confident statements based on that literature anyway.
