YOU SAID:

I have a banana for my brain

INTO JAPANESE

私は私の脳のバナナがあります。

BACK INTO ENGLISH

I have a banana in my brain.

INTO JAPANESE

私の脳にバナナがあります。

BACK INTO ENGLISH

My brain has a banana.

INTO JAPANESE

私の脳はバナナです。

BACK INTO ENGLISH

My brain is bananas.

INTO JAPANESE

私の脳はバナナです。

BACK INTO ENGLISH

My brain is bananas.