tDCS Cuts Reaction Time, Raises Mental Fatigue — SkimNews
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- Hongmei Xia at the University of Munich and colleagues recruited 31 volunteers with no known health conditions for a half-hour MRI session, including 20 minutes on the 3-back memory test; randomly chosen volunteers received active tDCS while unaware they were receiving it.
- tDCS produced faster and more accurate responses than sham stimulation, with average reaction times of 0.98 seconds versus 1.12 seconds, but the stimulated group also became more mentally fatigued afterward.
- Magnetic resonance spectroscopy found higher glutamate in the stimulated group’s dorsolateral prefrontal cortex, and higher glutamate was associated with a greater likelihood of choosing the €1 easy task over the €2 harder task.
- Hongmei Xia called the results the strongest evidence yet that mental fatigue results from glutamate buildup, said they support taking a break when mentally tired, and proposed testing the dorsolateral prefrontal cortex in people with depression.
- Emile Radyte said the study substantiates that stimulation made people work harder but does not prove higher glutamate caused fatigue; her Samphire Neuroscience trials found tDCS restored productivity when premenstrual syndrome hindered it, yet a 20-minute laboratory task does not establish a net productivity gain over a working day.
- Nilli Lavie of University College London called the study good but offered greater neural-energy use, rather than glutamate buildup, as an alternative explanation for the fatigue; she also said precise targeting without MRI guidance is difficult.
Why it matters: For the 31 volunteers with no known health conditions, stimulation delivered a task-level gain—0.98 seconds versus 1.12 seconds in average reaction time—but subsequent fatigue and the link between higher glutamate and choosing the €1 task over the €2 task mean the faster 20-minute result does not establish sustained productivity.
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