Nikhil Prasad Fact checked by:Thailand Medical News Team Aug 17, 2026 1 hour, 2 minutes ago
MRI Study Finds Brain Changes After COVID-19
A new brain imaging study suggests COVID-19 may be associated with measurable reductions in two important structures: the olfactory bulbs, which process smell, and the hippocampus, which is central to memory and learning.
MRI research links COVID-19 with smaller smell-processing and memory-related brain regions, especially among
patients reporting smell and taste loss
Researchers studied 60 people with confirmed COVID-19 and 54 people without COVID-19. Brain scans were performed one to three months after infection. Using detailed 3-Tesla MRI scans and stereological measurements, the team calculated olfactory bulb and hippocampal volumes.
Where the Researchers Are From
The researchers were from Ondokuz Mayıs University, Kastamonu University and Bolu Abant İzzet Baysal University in Türkiye. Their medical faculty departments included Histology and Embryology, Infectious Diseases, Radiology, Otolaryngology and Neurology.
Smell Loss Linked to Smaller Olfactory Bulbs
One of the clearest findings involved people who experienced loss of smell and taste. After adjustment for age and sex, COVID-19 patients with these symptoms had significantly smaller left, right and total olfactory bulb volumes than controls.
The differences were especially striking among women. Female COVID-19 patients with smell and taste loss had an average total olfactory bulb volume of 21.28 cubic millimeters, compared with 45.04 cubic millimeters among female controls. Their left olfactory bulb averaged 9.91 cubic millimeters versus 23.57 cubic millimeters in controls.
In this Thailand
Medical News report, an important distinction is that COVID-19 patients without smell and taste loss did not show statistically significant olfactory bulb reductions compared with controls after adjustment. This supports a possible connection between olfactory bulb changes and smell and taste dysfunction.
Hippocampus Changes Were More Widespread
The hippocampus showed a different pattern. Both male and female COVID-19 groups had smaller hippocampal volumes than controls, whether or not they reported losing smell and taste.
After adjustment for age and sex, left, right and total hippocampal volumes remained significantly lower in both COVID-19 groups. This suggests hippocampal changes may not simply result from losing smell.
Total hippocampal volume averaged 3,331.61 cubic millimeters in female COVID-19 patients with smell and taste loss and 3,062.74 in infected women without those symptoms. Female controls averaged 7,395.22 cubic millimeters. Male controls also had substantially larger hippocampal measurements than infected male groups.
What Could Be Causing the Changes?
The researchers discuss nervous-system inflammation and reduced sensory stimulation as possible explanations. Loss of smell may reduce normal activity in smell-related pathways, potentially contributing to structural changes, while inflammation may affect the hippocampu
s. However, the study did not prove the biological mechanism.
Important Limitations
The researchers caution that male groups were small, smell and taste problems relied on patient reports, and participants did not undergo formal cognitive testing. Smaller hippocampal volumes therefore cannot be considered direct proof of memory or thinking impairment.
Conclusions
The findings suggest COVID-19 may be associated with structural brain changes involving smell-processing and memory-related regions. Olfactory bulb reductions appear particularly connected to smell and taste loss, while hippocampal reductions were broader. Larger, long-term studies using objective smell tests and cognitive assessments are needed to determine whether these MRI changes persist, recover or cause meaningful neurological problems.
The study findings were published in the peer reviewed journal: Viruses.
https://www.mdpi.com/1999-4915/18/8/902
Read Also:
https://www.thailandmedical.news/articles/coronavirus
https://www.thailandmedical.news/articles/long-covid
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