Tilonus IV

From Memory Alpha, the free Star Trek reference.

Tilonus IV is a Class M planet that was home to a humanoid civilization with high curved forehead arches known as the Tilonians.

During the 2360s, the government of Tilonus IV was in a state of total anarchy when Commander William Riker attempted to rescue a Federation research team there in 2369. He was captured by one of the factions and subjected to neural manipulation by Suna at the Tilonus Institute for Mental Disorders in an attempt to extract tactical information from him. (TNG: "Frame of Mind")