Existential Reality is the source of true Truth, everything else is an attempt that shall fail inevitably, we only wish for them to linger long enough to facilitate a new generation of tries.

Trusted institutions and establishments are for whoever they serve. Identity and the stories we tell ourselves are closely related. Institutions and establishments provide a narrative. Everyone wants to believe their narrative is correct and meaningful, even when it is contradicted by those of others.

The answer to your riddle is that no one is a definitive source of "truth". A story of "truth" is a form of technology. The more consistently useful representation tends to prevail (of which astrological charts are as accurate as scientific predictions of human behavior.)

Notice that "more consistently useful" does not mean "true truth". Won't you invest in narratives that get you paid, or laid, or accepted?

True truth requires a cult like fastidious intention toward integrity (consistency) with existential Truths (observable, imperical, reproducible). Such austerity is not necessarily advantageous socially, economically, or politically.

To answer the other part of your question (downloading directly into our brain/nervous system), we don't. We hyper-train each ascendant brain in the brutal practice of undeceiving the self, and then either collect from curated sources (preprocessed informatica) or scrub first hand accounts for trace forensic Truth ourselves.

Information (resolve of uncertainty) is a valuable commodity. That is the nutritional basis for the ecosystem of autonomous, self discerning minds. It must be chosen carefully by taste and digested in the bowels of each and every comprehending mind.

The Foundation is the authority.

But to answer your question: Fake news can be discerned from true news by using the brain. Some have, some not.

The problem is, a brain alone is not enough. It must be prefilled with knowledge. So, universities and schooling becomes the basis. The next thing is to inter- and crosslink and use the knowledge, to derive the possibility for something. And then, it's possible to weight whether something is fake news or true news.

For example the organized children fighting in some basement of pizza restaurant. the loser will be eaten and it's blood is drank by Hillary - obviously, must be true.

Kamala being a man originally - wait, what? That milf? No wayyyyy it's true.

And so on.. in the end you should ask someone who has coined the term fake news :) Ex Mr. President Trump. He should be able to tell you what the difference is.