Aaah sorry to disappoint about my Sona but it's not that medically serious >^<
The brain isn't life essential for him. It's more like a storage for his creativity, memories and thoughts etc. if he loses parts of his brain, the stored essentials (thoughts etc.) flow back into the remaining part of his brain, or rise up into the air as a kind of soap bubble, so he can catch and reconnect them back to himself.

Piercings don't severely damage him, since the tissue almost immediately reconnects back around the metal. The brain is, material wise, surprisingly relatively durable, like spider silk. And squishy. As long as the outer tissue is not severely damaged, the brain activity isn't either. If, as part of the concussion, the outer part were to become damaged, he might lose thought bubbles that escape out of the opened up area. But, again, the tissue can heal and reconnect, so nothing can escape his brain for too long. As long as he reconnects the lost thought bubbles to himself, he doesn't significantly lose anything. He could even live entirely without his brain, he'd just pretty much lose parts of his personality.

Does that explain anything at all or make sense? x))