A Life Without Olfactory Function Has Limited Effects on Cerebral White Matter Morphology

Absence of sensory input is associated with alterations in brain morphology; mainly in or near cerebral regions normally devoted to processing of the missing sense. However, multiple recent studies demonstrate that the only consistent morphological finding within the gray matter of individuals born without the sense of smell (isolated congenital anosmia [ICA]), are changes in or near the olfactory sulcus. In contrast, for the connecting tissue of the brain, the white matter (WM), previous studies have yielded inconsistent findings. Here, we show that individuals with ICA (n = 49) exhibit clear alterations in WM volume when compared to age- and sex-matched controls. Consistent evidence from both voxel-based morphometry and multivoxel pattern analysis shows that individuals with ICA show decreased WM in areas surrounding the olfactory sulcus. Critically, no WM alterations were found in areas surrounding the olfactory (piriform) cortex. In contrast to congenital sensory loss in other sensory systems, we show that morphological alterations due to lifelong olfactory deprivation are limited, primarily localized around the olfactory sulcus, and likely due to the absence of olfactory bulbs. A possible explanation for the lack of major morphological alterations in individuals with congenital anosmia is that the olfactory regions may be recruited for nonolfactory functions.