How to find primary sources of information?

(Topic from @Ruslan82)

Certain nuclear divisions can be seen on the atlas Аlen of the human brain. For example, BNST is divided like this:

Снимок экрана 2020-11-03 в 10.45.47

I would like to understand on what principle such a division comes? Is there any original article, or is this an author’s division?

Of particular interest are the inputs / outputs to these divisions. I hope to find them when will find describing the principles by which such a division was made.

The same applies to two other nuclei: LSN (lateral septal nucleus), and PAG (periaqueductal gray substance).

Detailed references on the development and annotation of reference atlases (including delineation of anatomical boundaries) can be accessed in the publications, Supplemental Materials and Documentation associated with each atlas.