What is the sensation of exerting mental effort? It takes energy to think and focus attention, but we can’t directly feel what is going on in our brains. There are no sensory nerve endings in there. I can understand why we feel tired after thinking a lot, but I don’t understand why thinking hard feels effortful in the moment. It really does, though. Some of the thinking I’m doing feels like pushing a boulder up a hill, except more confusing, and my body aches with it–more than I would expect from just sitting and typing and looking at notes. My only idea is that I’m unconsciously flexing muscles when I think, especially in my face, neck, and back, and that produces the sensation of mental effort. What do you think? I’d sure like to be able to apply my brain fully without flexing any extra muscles.