Department of Physiology, Showa University School of Medicine, Tokyo, Japan.
Department of Otorhinolaryngology Head and Neck Surgery, Showa University School of Medicine, Tokyo, Japan.
Brain Behav. 2023 Apr;13(4):e2956. doi: 10.1002/brb3.2956. Epub 2023 Mar 10.
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.
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.
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.
Functional decline of the ENT and parahippocampus crucially impacts olfactory recognition. However, AMG function may compensate for deficits through connections with frontal regions.
在轻度认知障碍患者中，病理变化首先发生在杏仁核（AMG）和海马（HI），特别是在海马旁回和内嗅皮质（ENT）。这些区域在嗅觉检测和识别中起着重要作用。了解嗅觉障碍的细微迹象与上述区域以及眶额皮质（OFC）的功能之间的关系非常重要。在这项研究中，我们使用功能磁共振成像（fMRI）评估了大脑激活，在呈现嗅觉刺激（分类为“正常气味”，不引起记忆检索）时进行，并且研究了健康老年人的血氧水平依赖（BOLD）信号与嗅觉检测和识别能力之间的关系。
24 名健康老年人在嗅觉过程中进行了 fMRI，从感兴趣的区域中提取了原始平均 BOLD 信号，包括双侧区域（AMG、HI、海马旁回和 ENT）和眶额前区（额下回 OFC、额中 OFC、额中 OFC 和额上 OFC）。进行了多元回归和路径分析，以了解这些区域在嗅觉检测和识别中的作用。
左 AMG 的激活对嗅觉检测和识别的影响最大，而 ENT、海马旁回和 HI 则作为 AMG 激活的支持系统。右额内侧 OFC 的激活较少与良好的嗅觉识别相关。这些发现提高了我们对边缘和前额区域在老年人嗅觉意识和识别中的作用的理解。
ENT 和海马旁回的功能下降对嗅觉识别有重大影响。然而，AMG 功能可能通过与额叶区域的连接来补偿缺陷。
