It has been medically documented that people have been able to access previously unknown languages and even physical skills they didn’t originally possess when their brain has been damaged in some way, and such phenomena has also been documented in regards to recipients of organ transplants taking on traits of the person whose organ they received. Medical science and biology have no explanation for such things, and they are such rarities (they happen in something like 1% of cases) that they are just considered to be outliers, or coincidences.
There is so much about the human mind and brain that we just don’t know. Unlike other organs, we can’t study the brain outside of a living person to ascertain its functions so, while we know much about the physical structure of it, we really have no idea at all about its full capabilities. We do know the brain houses the personality (mainly because damage causes change to character traits. The Gage case is the most well documented) but the mind itself permeates the entire body and can cause real verifiable physical changes to it, self healing being the most obvious.
In his book Inner Alchemy, Taylor Ellwood talks about taking conscious control of autonomic functions, and talks about how he and a friend learned to take control of their adrenal system so they could access “super strength” at will.
As @Nyxifer said, it is hard to say whether spirits exist outside of us or not, but if you believe in Carl Jung’s concept of the collective unconscious, then it would make logical sense that the part of our mind that we call the subconscious can access the knowledge and possible skills available through it. If someone in the past did it, then it is possible for anyone to do it.