on the brain

Prepositional phrase

idiomatic

(idiomatic) Obsessively in mind.

Japanese Meaning

頭から離れず、いつも考えてしまう状態 / 気になって仕方がなく、常に頭にある

Ever since I heard that song, the chorus has been on the brain.

あの曲を聴いて以来、サビがずっと頭から離れません。

Sense（1）

(idiomatic) Obsessively in mind.

He's only got one thing on the brain: lust.