Olfactory performance and resting state functional connectivity in non‐demented drug naïve patients with Parkinson's disease

Olfactory performance in Parkinson's disease (PD) is closely associated with subsequent cognitive decline. In the present study, we analyzed the olfaction‐dependent functional connectivity with a hypothesis that olfactory performance would influence functional connectivity within key brain areas of PD. A total of 110 nondemented drug‐naïve patients with PD were subdivided into three groups of high score (PD‐H, n = 23), middle score (PD‐M, n = 64), and low score (PD‐L, n = 23) based on olfactory performance. We performed the resting‐state functional connectivity with seed region of interest in the posterior cingulate cortex (PCC) and caudate. An analysis of functional connectivity revealed that PD‐L patients exhibited a significant attenuation of cortical functional connectivity with the PCC in the bilateral primary sensory areas, right frontal areas, and right parietal areas compared to PD‐H or PD‐M patients. Meanwhile, PD‐L patients exhibited a significant enhancement of striatocortical functional connectivity in the bilateral occipital areas and right frontal areas compared to PD‐H or PD‐M patients. In the voxel‐wise correlation analysis, olfactory performance was positively associated with cortical functional connectivity with the PCC in similar areas of attenuated cortical connectivity in PD‐L patients relative to PD‐H patients. On the other hand, the cortical functional connectivity with the caudate was negatively correlated with olfactory performance in similar areas of increased connectivity in PD‐L patients relative to PD‐H patients. The present study demonstrated that resting state functional connectivity exhibits a distinctive pattern depending on olfactory performance, which might shed light on a meaningful relationship between olfactory impairment and cognitive dysfunction in PD. Hum Brain Mapp 36:1716–1727, 2015. © 2014 Wiley Periodicals, Inc.