Many COVID-19 patients experience neurological symptoms. These include loss of smell and delirium, with some reporting longer-lasting effects such as chronic fatigue syndrome and Guillan-Barre syndrome, a rare disorder in which your body's immune system attacks your nerves. But can COVID-19 also cause long-term memory loss and cognitive decline?
Although insufficient time has elapsed to answer this question conclusively, some suspect that it may indeed be the case.
The symptoms we have after contracting a virus are not directly caused by the virus. More often than not, they are simply immune responses. A general feeling of malaise, tiredness, and fever, for example, are caused by the activation of specialized immune cells in the brain, known as neuroimmune cells. These then cause behavioral changes that help the body fight the infection. Malaise and fatigue lead to more resting, giving the energy-demanding immune system more resources to get to work. Meanwhile, a fever makes the body less hospitable to viruses.
However, this specialized brain immune system also plays other roles. As it turns out, neuroimmune cells sit at the connections between brain cells (synapses), which are essential for memory formation. As they are activated by the COVID-19 virus, they may then be susceptible to damage, which may, in turn, harm our ability to form memories.
During periods of illness and inflammation, such as during COVID-19 infection, these specialized immune cells activate and deliver vast quantities of inflammatory signals. These signals cause microglia (a cell that gets rid of other cells waste products) to change shape and envelop pathogens or cell debris. In doing so, though, they also destroy and eat away neuronal connections vital for memory storage.
In this way, as the brain and immune system adapt according to experience to best fend off future dangers, COVID-19 may cause long-term changes in the brain's immune response. Should these changes be long-lasting, they may put people at an increased risk of age-related cognitive decline and Alzheimer's disease.
While whether this happens with COVID-19 remains unknown, a similar mechanism seems to be at work for other illnesses that result in cognitive decline. For example, many patients who recover from a heart attack report lasting cognitive defects that become more noticeable as they age. Even mild inflammation, such as that from chronic stress, is recognized as a risk factor for dementia and cognitive decline while aging.