From Beyond (1986)

Obsessive scientist Dr. Pretorius successfully discovers a way to access a parallel universe of pleasure by tapping into the brain's pineal gland. When he is seemingly killed by forces from this other dimension, his assistant, Dr. Crawford Tillinghast, is accused of the murder. After psychiatrist Katherine McMichaels and detective Bubba Brownlee take the case, the trio risks a return to the other world in order to solve the mystery.