Brains
Gray Matter
noun
Do you know みそ Soup and how miso goes in it? This is that miso. It's soft and strange feeling. Now, your brain miso, that's your brains or your gray matter. Essentially, if someone cuts your head open with a katana, this is perhaps what would come out.
Reading is just what you learned with the kanji. Just use your 脳 a bit and it should be easy.
少ない脳みそを使ってよく考えてみろ！
Try thinking carefully with what little brain you have!
今日はつかれすぎて脳みそが全然働いていません。
I'm so tired today, my brains just aren't working.
スマホ中毒じゃないよ。電池切れで何もしたくなくて、脳みそゼロでできるスマホのスクローリングでリラックスしてるんだよ。
I'm not addicted to my smartphone. When the battery runs out and I don't feel like doing anything, I relax by mindlessly scrolling through my phone with zero brain activity.