Out of the initial 435 studies, 111 studies investigating the neurocognitive impact of COVID-19 and its pathophysiology were examined. Several neuro-cognitive symptoms were reported; namely, executive dysfunction, memory loss, attention deficit, fatigue, anxiety, delirium, and processing speed delay. Other symptoms were also identified. The exact pathophysiological mechanism behind the cognitive effects is not clear. However, the review collected evidence that suggests several potential mechanisms. The virus may enter the central nervous system (CNS) through the olfactory nerve, vascular endothelial cells, or immune cells, breaking the blood-brain barrier by binding to the ACE2 receptor. Once in the brain, the virus can cause direct and indirect damage through various mechanismsThe review yielded that the combination of direct replication, immune-related inflammation involving cytokines as IL-6, TNFα, and IL-1β, immune dysregulation, vascular changes, low oxygen, brain hypometabolism, neurotransmitter imbalances, oxidative stress and amyloid deposit are responsible of the neurocognitive implications.
Interestingly, many studies showed that the cognitive impacts correlate with disease severity and psychiatric manifestations. Also, the studies emphasized the role of neuroimaging including 18F FDG PET scans (Positron Emission Tomography scans), in understanding the cognitive effects of COVID-19.