Marshall, P S, Forstot, M, Callies, A et al. · Psychosomatic medicine · 1997 · DOI
In a study comparing 20 ME/CFS patients with healthy controls and people with depression, researchers observed that ME/CFS patients performed more slowly on tests measuring reaction time and working memory—tasks that require fast cognitive processing. Notably, the effort of testing on day one did not worsen cognitive performance on day two. However, one important finding was that ME/CFS patients' test results looked similar to those of the depression group, even though the ME/CFS patients did not meet diagnostic criteria for depression.
This study provides objective evidence that cognitive complaints reported by ME/CFS patients—often dismissed as subjective—correlate with measurable slowing on standardised neuropsychological tests. The observation that performance did not worsen after exertion is relevant to understanding the relationship between cognitive effort and post-exertional symptom worsening in ME/CFS. The parallel cognitive slowing in both ME/CFS and depression raises questions about shared versus distinct neurobiological pathways.
This case–control design does not establish causation; it cannot determine whether cognitive slowing is caused by ME/CFS or is secondary to fatigue, deconditioning, or other factors. The study does not identify the underlying mechanism of cognitive slowing. The small sample size (N=20 per group) limits generalisability. The study is not a treatment trial and makes no claim about therapeutic interventions.
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 →
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