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慕尼黑大学 Hongmei Xia 团队在《美国科学院院刊》报告：用经颅直流电刺激提高背外侧前额叶兴奋性，可先提升高难度记忆任务表现，但随后降低人们选择高努力任务的意愿；磁共振波谱显示该区谷氨酸及谷氨酸–谷氨酰胺升高，并在统计上解释动机性疲劳。研究覆盖31名健康志愿者、约20分钟3-back任务；反应时约从1.12秒降至0.98秒。工作建立在2022年巴黎侧前额叶谷氨酸积累发现之上。Holroyd称其为因果研究；Pessiglione认为可排除纯心理解释但仍需纳入动机与信念；Radyte与Lavie提醒谷氨酸未必是唯一代价，短时实验不能证明工作日净收益。Scientific American 2026-11-04；New Scientist 2026-11-02；PNAS DOI 10.1073/pnas.2534136123。阅读时可留意 mental、fatigue、effort、reward、signal 等词，以及 may、suggest 如何保留证据边界。

正文

After hard mental work, many people lose the wish to keep going — even when more effort could bring a bigger reward. A new study led by Hongmei Xia at Ludwig Maximilian University of Munich offers a chemical account of that drop. The team reports that raising activity in a key control region improves memory performance at first, but also leaves people less willing to choose hard tasks afterward. The findings appear in the Proceedings of the National Academy of Sciences and were covered by Scientific American on 4 November 2026.

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辛苦动脑之后，许多人会失去继续坚持的意愿——哪怕多付出一些努力本可换来更大回报。慕尼黑大学 Ludwig Maximilian University 的 Hongmei Xia 带领的一项新研究，为这种下降提供了化学层面的解释。团队报告称：提高关键控制脑区的活动，起初能改善记忆表现，但随后会让人更不愿意选择困难任务。结果发表于《美国科学院院刊》（Proceedings of the National Academy of Sciences），并由《科学美国人》于2026年11月4日报道。

Scientists have long debated whether mental fatigue is mainly psychological or biological. In 2022, researchers in Paris linked sustained mental effort to a buildup of glutamate, a common signaling molecule, in the lateral prefrontal cortex. Xia’s group set out to test a stronger claim: that pushing this region harder can cause motivational fatigue through glutamate accumulation.

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科学家长期争论：脑力疲劳主要是心理现象，还是生物过程。2022年，巴黎研究者把持续脑力付出与谷氨酸（一种常见信号分子）在外侧前额叶皮层中的积累联系起来。Xia 团队想检验更强的主张：更用力推动这一脑区，可通过谷氨酸积累造成动机性疲劳。

Thirty-one healthy volunteers completed a demanding 20-minute 3-back memory test inside an MRI scanner on two separate days. In one session they received anodal transcranial direct current stimulation over the left dorsolateral prefrontal cortex; in the other they received a sham version. Before and after the test, they chose between easier tasks for smaller cash rewards and harder tasks for more money. The team also measured prefrontal glutamate with magnetic resonance spectroscopy.

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三十一名健康志愿者在两天内，分别在核磁共振扫描仪中完成约二十分钟的高难度 3-back 记忆测试。一次实验中，他们在左侧背外侧前额叶接受阳极经颅直流电刺激；另一次则接受假刺激。测试前后，他们要在“较容易任务换较少现金奖励”与“较难任务换更多钱”之间选择。团队还用磁共振波谱测量前额叶谷氨酸。

Active stimulation made people react faster and more accurately — average reaction time fell from about 1.12 seconds under sham to 0.98 seconds. Yet afterward they were less likely to select high-effort options for higher pay. Post-test glutamate and combined glutamate–glutamine levels were higher after real stimulation, and those rises statistically accounted for the drop in willingness.

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真刺激让人反应更快、更准确——平均反应时大约从假刺激下的1.12秒降到0.98秒。然而之后，他们更不倾向于选择高努力、高报酬的选项。真刺激后，测试结束时的谷氨酸以及谷氨酸–谷氨酰胺综合水平更高，而这些升高在统计上解释了意愿下降。

Xia suggests that the unpleasant feeling of mental fatigue may act as a safety signal, because large glutamate concentrations can harm cells. Outside expert Clay Holroyd called the work a causal study that fills an important piece of the puzzle. Mathias Pessiglione, senior author of the 2022 paper, said the results rule out a purely psychological explanation but still leave room for beliefs and goals. Emile Radyte and Nilli Lavie cautioned that glutamate may not be the only cost, and a short laboratory task does not prove a net benefit over a whole working day.

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Xia 提出：脑力疲劳那种不舒服的感觉，可能充当一种安全信号，因为高浓度谷氨酸可能损伤细胞。未参与研究的专家 Clay Holroyd 称这是一项因果研究，为拼图补上重要一块。2022年论文资深作者 Mathias Pessiglione 说，结果可以排除纯心理解释，但仍需纳入信念与目标。Emile Radyte 与 Nilli Lavie 提醒：谷氨酸未必是唯一代价，短时实验室任务也不能证明整个工作日有净收益。

The authors do not claim a ready treatment. For now, Xia’s advice is simple: switch to easier tasks and give the brain time to recover.

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作者并未宣称已有现成疗法。眼下 Xia 的建议很简单：改做较容易的任务，给大脑一些恢复时间。

新闻来源

• Scientific American · How does mental fatigue begin in the brain? (4 Nov 2026)
• New Scientist · Zapping part of the brain makes you think harder – at a cost (2 Nov 2026)
• Medical Xpress · A possible chemical explanation for why we give up on tough tasks (3 Nov 2026)
• PNAS · A causal account of the neural origins of mental fatigue (Xia et al.; DOI 10.1073/pnas.2534136123)

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