What impact does a viral infection have on our memory, attention, and concentration? The COVID-19 pandemic has reignited interest in this question, which has now been extended to other infections such as HIV, herpes, and hepatitis. A team from the University of Geneva (UNIGE) and Geneva University Hospital (HUG) reviewed over 900 scientific articles exploring the links between the immune system and cognitive functions. This analysis, published in Neuroscience & Biobehavioral Reviews, has identified several biological markers associated with cognitive decline in the context of infection. It also provides a solid foundation for future research.

Despite decades of research, the effects of viral infections on cognitive functions—such as memory, concentration, and attention—remain poorly understood. Most studies rely on comprehensive screening tools, applied individually to each disease. However, the emergence of the SARS-CoV-2 virus, along with the frequency and persistence of post-infectious cognitive sequelae, has reignited interest in this area of research.

In a new study, a team from UNIGE and HUG compiled and analysed the results of 931 scientific articles examining the links between the immune system and cognitive functions across various viral infections, including SARS-CoV-2, HIV, herpes, and hepatitis. ''Our goal was to take a cross-disciplinary approach to move beyond the fragmented perspective that prevails in this field,'' explains Julie Péron, associate professor at the Laboratory of Clinical and Experimental Neuropsychology, Faculty of Psychology and Educational Sciences, and at the Interfaculty Center for Affective Sciences, UNIGE, as well as a consulting neuropsychologist in the Neurology Service, Department of Clinical Neurosciences, HUG."

Several Biological ''Signatures'' Identified
This analysis confirms that persistent inflammation—initially a natural response by the body to an attack—could be linked to memory and concentration problems. More importantly, it highlights certain biological markers of the immune system associated with variations in cognitive performance. ''High levels of white blood cells called 'activated monocytes' and pro-inflammatory cytokines—proteins that enable the immune system to communicate—are correlated with a decline in episodic memory and information processing speed, '' says Anthony Nuber-Champier, a PhD student at the Laboratory of Clinical and Experimental Neuropsychology, Faculty of Psychology and Educational Sciences, and at the Interfaculty Center for Affective Sciences, UNIGE, as well as the lead author of the study."

Conversely, certain markers, such as activated CD4+ T cells—also white blood cells—or anti-inflammatory cytokines, seem to be associated with better preservation of cognitive abilities. ''However, immune responses vary from person to person. What appears to be decisive is the balance between these different inflammatory signals in maintaining long-term cognitive stability,'' the researcher points out.

A Solid Foundation for Future Research
These findings contribute to a better understanding of the cognitive disorders observed after certain infections and lay the groundwork for further investigation. They also confirm the conclusions of several clinical studies conducted in the context of long COVID, including the COVID Cog and Trajectory projects, in which UNIGE and HUG are actively involved. Funded by the Swiss National Science Foundation (SNSF), these projects aim to identify neuropsychological and neuropsychiatric deficits in post-COVID-19 patients.