They had developed a sophisticated virtual reality technology which tied in directly to their minds. Some time later, Prentaran scientists discovered another existence, a universe of the mind that supported, nurtured and augmented mental activity. They called it the thoughtscape and used it to enhance their VR technology by wiring the equipment into the interface between the universes.
Years later, the Prentara discovered that the thoughtscape was alive and stopped using it after a destructive pulse of energy emerged from the interface. A dark grey featureless substance also came out of the interface, being an extension of it, and eventually created cloud cover that completely surrounded the Prentaran planet. The Prentara called the beings that made up the thoughtscape the Inamuri. The Inamuri in turn considered the Prentara as both invaders and saviours.
Some time after this, in the late 22nd century the entire population of Prentara died. Most of those living in the cities nearest the interface site took their own lives. (DS9 - Mission Gamma novel: Twilight)