Our initial efforts to delve into the Codex Brain data provided us with a sequence of map coordinates. However, we still have fragments of the data that that the Codex attempted to destroy, which would imply a value to this data far beyond what we've discovered so far.
With time set aside to further analyze the data fragments leftover from our initial Codex experiment, I've finally managed to crack their code - and the resulting data is perhaps more valuable, and shocking, than I had expected. I understand now why the Codex was willing to sacrifice itself to protect this information.
In the shadows, the alien overseers, known to us as the "Elders," have continued to work in secret since the very beginnings of ADVENT. Although Central Officer Bradford tells me that no one has seen an Elder in the flesh for over a decade, we continue to see monuments in their likeness throughout the city centers. This is because they never left: they simply fell into the shadows, focusing their efforts on a more dire concern - the Elders are dying.
Among the diverse and widely varied alien specimens we've encountered, the Elders are uniquely afflicted by some form of rapid muscular degeneration. Their physical forms are no longer capable of containing the Psionic energy that is the Elders' lifeblood. Just as we've encountered these unique alien species in the field, at some point in the past, the Elders encountered them as well - and used them in an attempt to cure this plague among their own kind. Unfortunately for them, and for us, it seems they've never found this cure, and now it appears they are looking to use humanity as their next candidate. R. Tygan.