这事儿我已记在脑子里了。

I have got it right in my mind.

youdao

然后，我就把报纸带走。有了对这些词的理解，我就一遍又一遍地读那篇文章，这样那些词义就会牢牢地记在脑子里了。

Then I would take the paper away with me, armed now with the meaning of those words, and reread and reread the article so that the meaning of those words would get locked into my memory.

youdao

他把这个想法记在了脑子里，就像是一条以后再看的要点。

He catalogued this thought in his head like an entry in a capsule to be viewed at another time.

youdao

You don't have to do it on paper but take a moment to do it in your head.

你不用把指导语记在本子上,在脑子里想一想就可以了。

耶鲁公开课 - 心理学导论课程节选