Olfactory dysfunction affects over 20% of the global population, yet its neural underpinnings remain incompletely understood. This systematic review (Huang et al., 2026) synthesizes findings from 164 studies screened under PRISMA guidelines, encompassing structural MRI, diffusion tensor imaging (DTI), functional MRI, PET/SPECT, dopamine transporter imaging, and EEG. Structural MRI consistently demonstrated reduced olfactory bulb volume and sulcus depth, alongside gray matter loss in the orbitofrontal cortex, hippocampus, insula, and amygdala in acquired cases, while congenital anosmia paradoxically showed increases. DTI revealed widespread white matter abnormalities, particularly reduced fractional anisotropy. Functional imaging (fMRI) indicated heterogeneous global connectivity and reactivity changes, whereas PET/SPECT studies reported hypometabolism and reduced perfusion in frontal regions, especially orbitofrontal areas. Dopamine transporter imaging linked hyposmia to dopaminergic deficits in Parkinson’s disease and prodromal states. EEG studies, despite methodological variability, generally found prolonged latencies and reduced amplitudes in olfactory event-related potentials. Across modalities, correlations with olfactory function were low-to-moderate, reflecting etiological and methodological heterogeneity. The review emphasizes that olfactory dysfunction involves widespread neural alterations, with the orbitofrontal cortex consistently implicated. Future research should prioritize large-scale, standardized neuroimaging to enable stratified diagnosis and personalized prognosis.

Citation: Huang Y, Smeets PAM, Schrooten S, Boesveldt S. Neural correlates of olfactory dysfunction: A systematic review. Neurosci Biobehav Rev. 2026 Jul;186:106665. doi:10.1016/j.neubiorev.2026.106665. PMID: 41905561