Diodoro Sículo wrote that it was she who discovered the power of memory and that she gave names to many of the objects and concepts used to make mortals understand each other while talking. Mnemosyne was also the name of a river in Hades, in front of Lete, according to a series of Greek funerary inscriptions from the 4th century BC written in Dactyl hexameters. The souls of the dead drank Lete so that they would not remember their previous lives when they reincarnated. In Orphism, initiates were encouraged to drink from the river Mnemosyne, the river of memory, when they died, which would prevent the transmigration of the soul.
According to Pausânias, in Lebadeia in Boeotia there was the cave of Trophonius, which was one of the entrances to the underworld and where to enter it was necessary to first drink from two sources. The first, with the name of Lete (forgetfulness), made us forget about past things, while the other, with the name of Mnemosine, allowed us to remember what we would have seen in the afterlife. A similar procedure is described in the myth of Er at the end of Plato's Republic.