But what ridiculous science. The brains are smooth because all knowledge and memory have been drained? Fluid from the creature's eye stores visual memory?
Ummmmmm... no. Those plot developments were Ed Wood cringe worthy.
Still, it's a fun movie if you have time to kill.
It wasn't the creature's eye, it was the eye of a prehistoric man who was inhabited by the creature. When you have an extraterrestrial creature in your story, it gives you a lot of story latitude. Perhaps samples obtained from the inspector or the monk after the creature had inhabited their bodies would also yield similar images. If an alien being is able to reanimate an animal that has been dead and frozen for centuries, and can pull the mind out of a person through his eyes, then i would not doubt that it could smooth the crenellations of a brain.
This is a must-see movie, whether you have time to kill or not!