Cognitive Exhaustion
A recent study in Current Biology found that applying our cognitive resources to tedious, mentally taxing activities can lead to higher glutamate levels in our brains.
Glutamate is a signaling molecule that, when overabundant, can disrupt proper brain-function while also, seemingly, making cognitive tasks perceptually more difficult.
Said another way: when we apply our brains to tough problems or tasks, we accumulate more of this signaling molecule than our brains are meant to handle.
That overabundance can cause us to process things less capably, while also making other brain-related tasks seem more difficult—even if they would otherwise be well within our capacity to tackle, stress-free.
This study represents another link between neurometabolism (how our brains get and manage energy) and cognitive fatigue, which we might think of as mental exhaustion.
Previous research into a similar topic, sometimes referred to as "ego depletion," has been called into question following a flood of seemingly supportive research that later failed to replicate; which doesn't mean it's not a thing, it just means there's less research-backed reason to believe in it than previously seemed to be the case.
Ego depletion, in essence, says that as we mentally tax ourselves, we use up finite energy reserves (of glucose) and that lessens our capacity for self-control.
We might typically be capable of not lashing out at someone who offends us, but when we're cognitively exhausted, that ability might be diminished, leaving us more prone to angry outbursts, stress-eating, passively watching Netflix instead of working out or finishing our homework—all the things we maybe want to do on an animalistic level, but generally avoid doing because we have rational reasons to apply ourselves, elsewhere.
This new research differs from ego depletion in that it says we become cognitively fatigued when our glutamate levels are elevated, which messes with a neural system that moderates our capacity to choose long-term rewards over short-term gains—opting to exercise instead of eating cake, for instance.
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