noun
Colloquial term for the brain as a physical organ or tissue. Often used in casual conversation, sometimes with a slightly crude or humorous tone.
頭をぶつけて脳みそが飛び出しそうだ。
I hit my head so hard it feels like my brains are going to come out.
ゾンビ
Zombies apparently eat brains.
More formal and technical term for the brain. 脳みそ is colloquial and often used in everyday speech.
Compound of 脳 (nō, 'brain') and 味噌 (miso, 'fermented soybean paste'), likely from a metaphorical comparison of brain tissue to miso paste. The exact origin is uncertain.