Why is deliberate practice uncomfortable? For example, during learning college math and playing the piano. Why do we get headaches after long hours of practice?
According to this question, learning is about connecting distant neural networks; in forming these synapses resources are recruited such as calcium and glucose.
Now since the brain has no pain receptors, the discomfort must be coming from the surrounding nerves in the skull and neck. Possibilities:
a) Requiring greater resources is straining our blood system and hence the pain.
b) Forming many connections continuously creates excess of neurotransmitters such as glutamine that strain and literally swell brain areas, which in turn hit against our skull nerves.
Please feel free to correct me.
This topic is closely connected with the cellular mechanism of mental fatigue.