What is a biological explanation for Introverts need for recharging?

The same thing that happens in extroverts brains. Just a different charging source. Extroverts draw energy from social interaction. It feeds their brains and makes them feel energized. Introverts lose energy in social settings. Mental fatigue sets in if you are interacting with people a lot. The introvert “recharges” by being alone, doing quiet things, not having to deal with others.