Do brains get tired like muscles do?

Hannah - So, that feeling of fogginess that comes with brain fatigue. You've probably experienced it at some point. Scientists haven't yet figured out the exact biochemical pathway leading to it, but it seems to be linked to, perhaps unsurprisingly, how much you use your brain and how much fuel it has available. Here's Dr. Catherine Hall, brain energy expert from University College London explaining what happens when muscles in your body get tired from too much exercise.

Catherine - When we've been exercising, lactic acid does build up in our muscle. But actually, it probably doesn't cause the pain and muscle fatigue we feel after exercising. Instead that is caused by a shortage of fuel and a build-up of lots of different molecules that are by-products of muscle activation. Lactic acid may be one of these molecules or it may actually reduce muscle tiredness. In our brains, lactic acid also builds up when nerve cells are active. But nerve cells can use lactic acid as a fuel. So, while it might be a sign of an active brain, if anything it should stop our brains from being tired.

Hannah - Aha! So, activating our brains actually provides a short burst of lactic acid which is an actual fuel for our brain. So, that shouldn't cause fogginess or brain fatigue. But surely, this fuel burst will wear out at some point.

Catherine - We do get tired though and it turns out, a good dose of glucose does boost brain performance. And handily, eating some glucose it particularly good at boosting our ability to do tasks that use verbal memory so it'll especially help you to do your French homework. You have to be careful though as too much glucose will stop your brain working so well. By eating 38 M&Ms before starting your homework, you should get a brain boost that will last you an hour or so. Watch out though. Your brain isn't actually burning all that extra energy so French homework won't stop you getting fat.

Hannah - Thank you, Catherine. She also adds that she doesn't want to be responsible for everybody reaching for the candy and worldwide surge in type 2 diabetes with this answer. She does suggest that healthier, slow release glucose treats, like maybe a banana, could also boost brain power, or you could just take a break to refocus your mind.