Under high exertion or stress, certain brain regions like the hypothalamus and brain stem preferentially utilize lactate and glucose, leading to a temporary quieting of the prefrontal cortex.

“My understanding about the distribution of neurons that preferentially use lactate as a fuel under conditions of let's say high stress but also just High exertion doesn't have to be stressful is that for somewhat obvious reasons the hypothalamus and areas of the brain stem that control breathing and more primitive functions are going to utilize that fuel preferentially first and this is actually evident when for instance you get into an ice bath or any kind of adrenaline shock environment the what little neuroimaging is out there tells us that the prefrontal cortex which is involved in kind of rule setting and decision making but really Rule and contingency setting we could talk more about this essentially shuts down but doesn't shut down because of lack of electrical activity it shuts down because there's a preferential shuttling of glucose and lactate to other regions of the brain that just need to keep everything online”