Fig. 4.

Comparisons between COVID-hyposmia on one side and COVID-non-hyposmia and PD-hyposmia respectively. COVID-hyposmia patients showed significant hypometabolism with respect to COVID-non-hyposmia in a bilateral and symmetric cluster encompassing gyrus rectus and inferior, middle, and superior frontal gyrus (A) while (changing the direction of the contrast) no regions of significant hypometabolism were identified in COVID-non-hyposmia. With respect to PD-hyposmia patients COVID-hyposmia patients showed hypometabolism in middle and superior temporal gyri, medial, and middle frontal gyri on both hemispheres and right insula (B). PD-hyposmia patients showed relative hypometabolism with respect to COVID-hyposmia in wide cortical regions mainly involving inferior and middle occipital gyri and cuneus in both hemispheres (C). Clusters with significant hypometabolism are shown superimposed on an MRI template. The color bars indicate the level of z-scores for significant voxels. (See Tables 3 and 4 for details on coordinates and z-scores.)