I don't have a text handy for it, but that's what our catechist taught us. The nous is the part of you that can stand back and be aware of your thoughts, in an almost third-person kind of way. And one of the things you're trying to do when saying the Jesus prayer, is draw that awareness down from the head into the heart.

Here's a bit from St. Vlad's that at least hints at it, though doesn't state it so explicitly as my catechist. Look in the "prayer of the heart" section:

https://www.svots.edu/saying-jesus-prayer