Role of the amygdala‐medial orbitofrontal relationship in odor recognition in the elderly

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  • Kei Sakikawa
    Department of Physiology Showa University School of Medicine Tokyo Japan
  • Yuri Masaoka
    Department of Physiology Showa University School of Medicine Tokyo Japan
  • Motoyasu Honma
    Department of Physiology Showa University School of Medicine Tokyo Japan
  • Akira Yoshikawa
    Department of Physiology Showa University School of Medicine Tokyo Japan
  • Masaki Yoshida
    Department of Ophthalmology Jikei Medical University Tokyo Japan
  • Sawa Kamimura
    Department of Physiology Showa University School of Medicine Tokyo Japan
  • Masahiro Ida
    Department of Radiology National Hospital Organization Mito Medical Center Ibaraki Japan
  • Hitome Kobayashi
    Department of Otorhinolaryngology Head and Neck Surgery Showa University School of Medicine Tokyo Japan
  • Masahiko Izumizaki
    Department of Physiology Showa University School of Medicine Tokyo Japan

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<jats:title>Abstract</jats:title><jats:sec><jats:title>Introduction</jats:title><jats:p>In patients with mild cognitive impairment, pathological changes begin in the amygdala (AMG) and hippocampus (HI), especially in the parahippocampal gyrus and entorhinal cortex (ENT). These areas play an important role in olfactory detection and recognition. It is important to understand how subtle signs of olfactory disability relate to the functions of the above‐mentioned regions, as well as the orbitofrontal cortex (OFC). In this study, we evaluated brain activation using functional magnetic resonance imaging (fMRI), performed during the presentation of olfactory stimuli (classified as “normal odors” not inducing memory retrieval), and investigated the relationships of the blood oxygen level‐dependent (BOLD) signal with olfactory detection and recognition abilities in healthy elderly subjects.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>Twenty‐four healthy elderly subjects underwent fMRI during olfaction, and raw mean BOLD signals were extracted from regions of interest, including bilateral regions (AMG, HI, parahippocampus, and ENT) and orbitofrontal subregions (frontal inferior OFC, frontal medial OFC, frontal middle OFC, and frontal superior OFC). Multiple regression and path analyses were conducted to understand the roles of these areas in olfactory detection and recognition.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>Activation of the left AMG had the greatest impact on olfactory detection and recognition, while the ENT, parahippocampus, and HI acted as a support system for AMG activation. Less activation of the right frontal medial OFC was associated with good olfactory recognition. These findings improve our understanding of the roles of limbic and prefrontal regions in olfactory awareness and identification in elderly individuals.</jats:p></jats:sec><jats:sec><jats:title>Conclusion</jats:title><jats:p>Functional decline of the ENT and parahippocampus crucially impacts olfactory recognition. However, AMG function may compensate for deficits through connections with frontal regions.</jats:p></jats:sec>

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