Olfactory loss and brain connectivity after COVID-19

Area of Science:

• Neuroscience
• Neuroimaging
• Olfactory System Research

Background:

• COVID-19 (Coronavirus disease 2019) is known to cause olfactory dysfunction, including hyposmia (reduced sense of smell).
• The neurological underpinnings of persistent olfactory loss following SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) infection remain incompletely understood.
• Investigating central olfactory system neural connectivity is crucial for understanding the brain's response to COVID-19-related olfactory impairment.

Purpose of the Study:

• To analyze neural connectivity within the central olfactory system of individuals experiencing residual olfactory impairment after COVID-19.
• To compare structural and functional brain connectivity metrics between recently SARS-CoV-2 infected subjects with hyposmia and healthy controls.
• To correlate neural connectivity patterns with the severity of olfactory impairment.

Main Methods:

• Recruited 27 subjects with confirmed COVID-19-related hyposmia and 18 healthy normosmic controls.
• Utilized 3 Tesla MRI, including high angular resolution diffusion imaging (HARDI) and resting-state functional MRI (rs-fMRI).
• Derived structural and functional connectivity metrics using a standard olfactory brain parcellation and a graph-theoretic model, comparing groups and correlating with olfactory impairment indices.

Main Results:

• Significantly increased structural and functional neural connectivity metrics were observed in previously SARS-CoV-2 infected subjects compared to controls.
• Greater residual olfactory impairment correlated with more segregated processing, particularly in regions connected to the anterior piriform cortex.
• Increased olfactory cortex neural connectivity was associated with recent SARS-CoV-2 infection and residual olfactory loss, with anterior piriform cortex connectivity explaining sensory impairment variability.

Conclusions:

• Recent SARS-CoV-2 infection associated with residual olfactory loss shows increased neural connectivity within the olfactory cortex.
• The functional connectivity of the anterior piriform cortex plays a key role in the variability of olfactory sensory impairment.
• These findings suggest a characteristic brain connectivity response to COVID-19-related residual hyposmia, warranting further investigation.