Conservation of energy leads to Bernoulli's principle which is essential for understanding aerodynamics and the flight of a bird. In the same way I feel like conservation of energy must operate in the brain at least on certain timescales. Obviously net energy comes in via the bloodstream but what if neurons were able to directly reward each other with energy, forming a kind of activity market? Further research tells me this is unlikely however I did learn that often-used neurons and connections get optimized to be faster and more efficient.