Cognitively-induced PEM might depend on the specific cognitive activity, and vary with the individual. One person might trigger on visual processing, while another on word-searching or math. I think emotional triggers are also common, although I'm not sure what level of processing is involved. Maybe some hormones cause more processing in other parts of the brain? For me, driving was a trigger, and the more stressful the driving conditions (dark, snowy, icy roads), the worse the PEM. Chatting with someone was another trigger.
For someone who is interested, and has suitable cognitive triggers, maybe keep track of the specifics that trigger PEM to what degree. Maybe font properties are a factor. Maybe word selection ( a book for children vs one for adults by an author who wants to show off his obscure word knowledge), or an easy-to-read cookbook vs a book on quantum physics. Emotional activities vs non-emotional ones. Maybe there's some useful information to be found by such investigation.
My physically-induced PEM depended on how unusual the muscle usage was, which I hypothesize means how much muscle damage was done, and thus how much the immune cells activated. Climbing a few rungs up a ladder (after not doing it for a long time) would trigger PEM, whereas a multi-hr bike ride wouldn't, if I was used to riding. There might be something similar for cognitive triggers.
