The brain matter is indeed pierced. While “you only use 10% of your brain” is a myth, much of the brain is what we call non-eloquent, meaning it can be damaged or removed without any noticeable effects. Especially when it just means being pierced by a 2-3mm diameter lead. Are there hidden side effects that we are simply unable to recognize? Sure, but with as primitive an understanding of the brain as we currently have, we are forced to rely on a more pragmatic rather than philosophical approach.