A recent study showed that people who lost their sense of smell during infection with Covid-19 showed changes in their behaviour, brain function and structure.

Chilean researchers examined cognitive abilities, decision-making and brain function using magnetic resonance imaging (MRI) on 73 patients with mild to moderate COVID-19 and compared them with 27 individuals who were infected for other reasons.

These tests were conducted approximately nine months after COVID-19 diagnosis, and follow-up sessions were held at an interval of 15 days.

The average age of the participants was 40.1 years. The study was conducted with patients recruited from hospitals in Santiago between February 2020 and May 2023.

The study, published in Scientific Reports, used loss of smell as an indicator of possible brain involvement and the need for hospitalization as an indicator of disease severity.

Key findings of the study

• Of the 73 COVID-19 patients, 30.1% reported memory and attention problems, with some also experiencing headaches, fatigue or loss of smell, which lasted for about 1.3 months on average.
• Of those who lost their sense of smell, 68% lost their sense of smell completely, while the rest reported changes in their sense of smell.
• Tests found that of the 43 patients who lost their sense of smell during the infection, 6 were only able to identify four out of six odors, a sign of persistent illness.
• The study found that patients who had lost their sense of smell were more impulsive in decision-making tasks and were more likely to change their choices after a negative outcome. MRI scans revealed that these patients had reduced brain activity during decision-making, decreased white-matter integrity, and thinner outer layers of the brain in regions responsible for processing sensory information and spatial awareness.

The researchers concluded that anosmia (loss of sense of smell) may be a sign of virus-induced brain damage and may indicate that individuals are at risk for neurological problems.

Further research is needed to determine the extent of COVID-related brain damage associated with loss of smell, its potential as a marker of susceptibility to various brain disorders, and to explore potential treatment targets.