Brain fog in Parkinson’s disease: unraveling mechanisms and measuring impact

Inconsistent colloquial and professional uses of the term "brain fog" have undermined the potential for empirical study of this symptom complex, and there is no consensus about how to diagnose or treat it. Yet brain fog is frequently reported by patients with post-acute sequelae of SARS-CoV-2 (PASC) and other chronic conditions, often presenting as cognitive difficulties such as memory issues and attention deficits, accompanied by central fatigue and sometimes depression. This symptom complex is also common in Parkinson's disease (PD). One objective of this article is to propose a theoretical model that conceptualizes brain fog in PD in terms that can guide its measurement and treatment. Neuroinflammation, dopaminergic dysfunction, and immune system interactions are examined as potential mechanisms. We present the Fatigue and Altered Cognition Scale (FACs), a patient-report tool designed to assess brain fog in clinical and research settings that has been validated in traumatic brain injury and PASC. Proper diagnosis and monitoring of brain fog are important because early research suggests that existing medications, such as methylphenidate, and natural substances, such as carnosic acid, have the potential to alleviate its symptoms. Ongoing research is crucial to establish a clear definition of brain fog and identify effective treatments in PD and other neurodegenerative disorders.