Japanese Body Language -

頭におく[あたまにおく, atama ni oku] take under consideration

oku is to place or put.

If you need to give something some thought, what better thing is there to do than to put it in your head.

Stick it in your mind to mull on later. 

Set it on the shelf in your head to dig out.

When asking a Japanese to do something they aren’t inclined to, they may respond that they will think on it in this way. But, don’t expect an answer. In Japan, no answer is often the answer no.