Nuclear medicine and functional magnetic resonance imaging studies have shown that mild cognitive impairment (MCI) and dementia, including Alzheimer's disease (AD), are characterized by changes in cerebral blood flow. This article reviews the application of an alternative method, functional near-infrared spectroscopy (fNIRS), to the study of cerebral oxygenation changes in MCI and dementia. We synthesized 36 fNIRS studies that examined hemodynamic changes during both the resting state and the execution of tasks of word retrieval, memory, motor control, and visuospatial perception in MCI and dementia. This qualitative review reveals that (amnestic) MCI and AD patients have disrupted frontal and long-range connectivity in the resting state compared to individuals with normal cognition (NC). These patients also exhibit reduced frontal oxygenation changes in various cognitive domains. The review also shows that disrupted connectivity and decreased frontal oxygenation levels/changes are more severe in AD than in (amnestic) MCI, confirming that MCI is an intermediate stage between NC and dementia. Thus, there is reduced resting frontal perfusion, which is greater than expected for age, and a lack of frontal compensatory responses to functional decline across cognitive operations (i.e., word retrieval and memory functioning) in MCI and AD. These indices might potentially serve as perfusion- or oxygenation-based biomarkers for MCI/dementia. To expand the utility of fNIRS for MCI and dementia, further studies that measure tissue oxygenation in a wider range of brain regions and cognitive domains, compare different MCI and dementia types, and correlate changes in cerebral oxygenation over time with disease progression are needed.

中文翻译：

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功能性近红外光谱显示轻度认知障碍和痴呆症中的静息氧合水平降低和与任务相关的氧合变化：系统综述。

核医学和功能性磁共振成像研究表明，轻度认知障碍（MCI）和痴呆症（包括阿尔茨海默氏病（AD））的特征是脑血流的变化。本文回顾了功能性近红外光谱（fNIRS）替代方法在研究MCI和痴呆症中脑氧合变化中的应用。我们合成了36个fNIRS研究，研究了MCI和痴呆症的静息状态和单词检索，记忆，运动控制以及视觉空间感知任务的执行过程中的血液动力学变化。这项定性研究表明，（记忆）MCI和AD患者与具有正常认知（NC）的个体相比，在静息状态下破坏了额叶和远距离的连接。这些患者在各个认知领域也表现出减少的额叶氧合变化。该评价还表明，AD的连接性破坏和额叶氧合水平降低/变化比（遗忘）MCI更为严重，这证实了MCI是NC和痴呆之间的中间阶段。因此，在MCI和AD中，静息额叶灌注减少，这比年龄预期的要大，并且缺乏对认知操作（即单词检索和记忆功能）中的功能下降的额叶代偿反应。这些指数可能潜在地充当基于灌注或氧合作用的MCI /痴呆症生物标志物。为了扩大fNIRS在MCI和痴呆症中的应用，需要进行进一步的研究以测量更广泛的大脑区域和认知区域的组织氧合作用，比较不同的MCI和痴呆症类型，