We've all seen them, but what were they for? Were they fasteners used to hold Mary Shelley's creature's head on, which would be suspicious, since she didn't use bolts to attach it's limbs, or were they merely used as conduits to route the energy needed to reanimate Dr. Frankenstein's creation?
The bolts, green complexion and low IQ are all attributes that were added in the films. In the original gothic novel, Shelley's creature is loving, well-read, and intelligent. He becomes vengeful and monstrous only after his repeated attempts at acceptance and love are rejected.
I think it was a way to transfer the electricity from the lightning through the creature's body, and into it's heart, reanimating it thusly