Recent implications of glutamatergic signaling in a wide range of psychiatric disorders has highlighted the need to study the dynamics of glutamate (Glu) in the brain outside of steady state. A promising modality for doing so is functional Magnetic Resonance Spectroscopy (fMRS). Recent human studies at high magnetic fields (7T) have reported small but consistent changes in metabolite concentrations, in particular a 2-4% increase in Glu during visual and motor stimulation. While the origins of these changes remain the topic of ongoing research, the ability of fMRS to observe metabolites directly associated with neurotransmission and brain energetics could potentially aid our understanding of brain pathophysiology and the interpretation of functional imaging experiments. For this to happen, the current ultrahigh field results must be reproduced at lower, widely available clinical field strengths, in response to a wide variety of stimuli classes. Our goal herein was to investigate metabolite changes during a hand-clenching motor task at 3T, and to investigate the effect of the stimulation's temporal characteristics on the magnitude of the fMRS changes; specifically, we compared two block-designed functional activation paradigms, using short- and long-cycled clenching designs. Small but statistically significant increases in Glx=Glutamate+Glutamine (3.8%) and Glu (4.0%) concentrations were detected during the long-cycled design, while no statistically significant changes were observed during the short-cycled design. Activation during the long-cycled tasks was correlated to the frequency of clenching. We have also shown that using subject-level analysis in combination with a linear mixed model increases the observed effect size, and could help analyzing the weak MRS signals. Our results are in good agreement with the previous reports acquired at higher field systems, and support the viability of fMRS as a research tool at clinical field strengths, while also emphasizing the importance of the functional paradigm itself.

中文翻译：

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使用 3T 的功能性磁共振波谱测量在长时间运动激活期间增加的谷氨酸浓度

谷氨酸能信号在广泛的精神疾病中的最新影响凸显了研究稳态以外大脑中谷氨酸 (Glu) 动力学的必要性。一种很有前景的方法是功能磁共振光谱 (fMRS)。最近在高磁场 (7T) 下的人体研究报告了代谢物浓度的微小但一致的变化，特别是在视觉和运动刺激期间 Glu 增加了 2-4%。虽然这些变化的起源仍然是正在进行的研究的主题，但 fMRS 观察与神经传递和脑能量学直接相关的代谢物的能力可能有助于我们理解脑病理生理学和功能成像实验的解释。要做到这一点，当前的超高场结果必须在较低的、广泛可用的临床场强下重现，以响应各种刺激类别。我们在此的目标是研究 3T 下握紧手运动任务期间的代谢物变化，并研究刺激的时间特征对 fMRS 变化幅度的影响；具体而言，我们使用短周期和长周期紧握设计比较了两种块设计的功能激活范式。在长周期设计期间检测到 Glx=谷氨酸 + 谷氨酰胺 (3.8%) 和 Glu (4.0%) 浓度的小但统计上显着的增加，而在短周期设计期间没有观察到统计上的显着变化。长周期任务期间的激活与握紧的频率相关。我们还表明，将受试者水平分析与线性混合模型结合使用会增加观察到的效应大小，并有助于分析微弱的 MRS 信号。我们的结果与之前在更高领域系统中获得的报告非常一致，并支持 fMRS 作为临床领域研究工具的可行性，同时也强调了功能范式本身的重要性。