A localized region of the brain allows you to switch focus, at a cost of some energy.
The Attentional Switch is part of the Human Attentional System, which allows the Central Executive function to focus on one thing wholly, then bridge over to a new thing.
Operating the switch (changing your focus) takes literal cellular energy. This is related to Context Loading and is part of the reasons behind Decision Fatigue.
The switch apparently is localized to a certain spot within the brain.