Woodcock Eric A, Anand Chaitali, Khatib Dalal, Diwadkar Vaibhav A, Stanley Jeffrey A
Brain Imaging Research Division, Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, MI, United States.
Front Psychiatry. 2018 Mar 6;9:66. doi: 10.3389/fpsyt.2018.00066. eCollection 2018.
Glutamate is involved in excitatory neurotransmission and metabolic processes related to brain function. Previous studies using proton functional magnetic resonance spectroscopy (H fMRS) have demonstrated elevated cortical glutamate levels by 2-4% during visual and motor stimulation, relative to periods of no stimulation. Here, we extended this approach to working memory cognitive task performance, which has been consistently associated with dorsolateral prefrontal cortex (dlPFC) activation. Sixteen healthy adult volunteers completed a continuous visual fixation "rest" task followed by a letter 2-back working memory task during H fMRS acquisition of the left dlPFC, which encompassed Brodmann areas 45 and 46 over a 4.5-cm volume. Using a 100% automated fitting procedure integrated with LCModel, raw spectra were eddy current-, phase-, and shift-corrected prior to quantification resulting in a 32s temporal resolution or 8 averages per spectra. Task compliance was high (95 ± 11% correct) and the mean Cramer-Rao Lower Bound of glutamate was 6.9 ± 0.9%. Relative to continuous passive visual fixation, left dlPFC glutamate levels were significantly higher by 2.7% (0.32 mmol/kg wet weight) during letter 2-back performance. Elevated dlPFC glutamate levels reflect increased metabolic activity and excitatory neurotransmission driven by working memory-related cognitive demands. These results provide the first demonstration of elevated dlPFC glutamate levels during working memory.
谷氨酸参与与脑功能相关的兴奋性神经传递和代谢过程。以往使用质子功能磁共振波谱（H fMRS）的研究表明，在视觉和运动刺激期间，皮质谷氨酸水平相对于无刺激期升高了2 - 4%。在此，我们将这种方法扩展到工作记忆认知任务表现，工作记忆一直与背外侧前额叶皮质（dlPFC）激活相关。16名健康成年志愿者在对左侧dlPFC进行H fMRS采集期间，先完成了一个持续视觉注视的“休息”任务，随后完成了一个字母2 - 回溯工作记忆任务，采集区域覆盖了45和46 Brodmann区，体积为4.5厘米。使用与LCModel集成的100%自动化拟合程序，在量化之前对原始光谱进行了涡流、相位和偏移校正，从而得到32秒的时间分辨率或每个光谱8次平均。任务完成率很高（正确度为95 ± 11%），谷氨酸的平均克莱姆 - 拉奥下限为6.9 ± 0.9%。相对于持续被动视觉注视，在字母2 - 回溯任务执行期间，左侧dlPFC谷氨酸水平显著升高了2.7%（0.32 mmol/kg湿重）。dlPFC谷氨酸水平升高反映了由工作记忆相关认知需求驱动的代谢活动增加和兴奋性神经传递增强。这些结果首次证明了在工作记忆期间dlPFC谷氨酸水平升高。
