Olfactory network reorganization in Parkinson's disease.

INTRODUCTION

: Olfactory dysfunction is an early hallmark for Parkinson’s disease (PD) patients. Though clinical work has identified hyposmia/anosmia as early prodromal symptoms, the underlying brain functional network remains under-researched.

METHODS

Using collected resting state functional MRI (rsfMRI) from 20 PD and 23 controls, we used a graph theoretical analysis (GTA) approach to identify disrupted connectivity. PD subjects were tested using the University of Pennsylvania Smell Identification Test (UPSIT). We reproduced a previously validated olfaction network (OlfN) at multiple threshold values and calculated network metrics, including efficiency and centrality measures. We also used Network-Based Statistics (NBS) to test impacted graph components.

RESULTS

We identified significantly reduced efficiency in the right OlfN for multiple thresholds. Using NBS, we identified the olfactory orbitofrontal cortex (Oolf) as a key impacted region. We also found that the Oolf had significantly reduced node strength and betweenness centrality. No significant correlation between UPSIT score and olfactory efficiency was found, but a significant correlation exists if the only PD subject with normal olfaction is removed from analysis. We tested the occipital network as a control, and found no significant group differences, suggesting network damage was specific.

CONCLUSIONS

: Our work identified reduced right OlfN efficiency in PD compared to a control group, which suggests systematic loss of function in the network. We identified that the Oolf, a region particularly important for analysis of incoming sensory information, is particularly impaired in PD. This study provides new insights into PD-related network disruptions and their role in olfactory deficits.