The player runs into the talking brain three times. It must be attacked in order to proceed.
After attacking it The Siren will spawn and it will have to be lured away in some way in order to progress in the area.
"What are you hoping to accomplish? Without me, you're just hollow. You're pathetic. You need fear to motivate you."
"Do you think you're getting better? Does doing this even have a purpose?"
"I'm your identity! I'm your crutch! You used to cling to me like a parasite. I know you better than anyone. And I know you're weak. You'll come right back."
The Talking Brain appears to be a manifestation of the protagonist's feeling of worthlessness as well as their self-doubt. The Brain's berating of the player could also be a representation of the protagonist's implied abusive relationship.