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Advanced Neurology

ORIGINAL RESEARCH ARTICLE
The most significant brain regions implicated in

olfactory dysfunction in Parkinson’s disease

Naser Moradi 1 , Siamak Shahidi * , Bahareh Zaker Harofteh * ,
2
3
Mohammad Ahmadpanah 4 , Sajjad Farashi 2 , and Ghodratollah Roshanaei 5
1 Department of Neuroscience, School of Science and Advanced Technologies in Medicine, Hamadan
University of Medical Sciences, Hamadan, Iran
2 Neurophysiology Research Center, Institute of Neuroscience and Mental Health, Avicenna Health
Research Institute, Hamadan University of Medical Sciences, Hamadan, Iran
3 Department of Neurological Disease, Shahid Beheshti University of Medical Sciences, Tehran, Iran
4 Behavioral Disorders and Substance Abuse Research Center, Institute of Neuroscience and Mental
Health, Avicenna Health Research Institute, Hamadan University of Medical Sciences, Hamadan,
Iran
5 Department of Biostatistics, School of Medicine, Arak University of Medical Sciences, Arak, Iran

Abstract
Olfactory dysfunction is observed in over 95% of patients with Parkinson’s disease
(PD). This study examines the relationship between gray matter volume (GMV) and
olfactory impairment in a cohort of 182 subjects, including PD patients and healthy
*Corresponding authors: controls (HCs). Using the Iran Smell Identification Test, which is a standardized 24-item
Siamak Shahidi olfactory identification assessment, to evaluate the olfactory performance, PD
(n.moradi@edu.umsha.ac.ir)
Bahareh Zaker Harofteh patients were divided into two groups (scores ranging from 0 to 18 indicate olfactory
(bahar.zaker.h@gmail.com) dysfunction, while scores from 19 to 24 indicate normal olfaction): those with normal
Citation: Moradi N, Shahidi S, smell (PD-NS, n = 23) and those with smell disorders (PD-SD, n = 69). Differences
Harofteh BZ, Ahmadpanah M, in GMV were analyzed using voxel-based morphometry. Statistical analysis was
Farashi S, Roshanaei G. The conducted using SPSS 26. The results revealed that the PD-NS group exhibited
most significant brain regions
implicated in olfactory dysfunction reduced GMV in the right thalamus and the left parahippocampal gyrus compared
in Parkinson’s disease. Adv Neuro. to the HCs. Furthermore, the HC group demonstrated no statistically significant
2025;4(3):60-69. olfactory dysfunction. In contrast, the PD-SD group showed significant decreases
doi: 10.36922/AN025110024
in GMV in the right entorhinal cortex and both the right and left hippocampus
Received: March 16, 2025 compared to both the HC and PD-NS groups. These findings indicate that PD patients
Revised: April 12, 2025 experience more severe olfactory dysfunction in hippocampal regions than the HC
group, likely attributed to the initial pathological loss of gray matter in both the right
Accepted: April 17, 2025
and left hippocampus.
Published online: May 20, 2025
Copyright: © 2025 Author(s). Keywords: Parkinson’s disease; Smell; Gray matter; MRI; Brain volumetry
This is an Open-Access article
distributed under the terms of the
Creative Commons Attribution
License, permitting distribution,
and reproduction in any medium, 1. Introduction
provided the original work is
properly cited. Parkinson’s disease (PD) is a chronic and progressive neurodegenerative condition
Publisher’s Note: AccScience that predominantly affects the dopamine-producing neurons in the substantia nigra,
Publishing remains neutral with resulting in the development of motor symptoms. PD is acknowledged as a multifaceted
1
regard to jurisdictional claims in
published maps and institutional condition that impacts various systems and is marked by a range of both motor and
affiliations. non-motor symptoms, including deficits in olfaction. Among the non-motor symptoms

Volume 4 Issue 3 (2025) 60 doi: 10.36922/AN025110024