I remember that one of the main characters was a researcher into psychic abilities. He went to a remote Scottish location following reports of a girl with special abilities and found her, living like an animal because she was so overwhelmed by hearing everyone's thoughts. He helped her gain control of her powers using sensory deprivation. He also developed abilities, and so did several other people that joined their team. There was a Russian boy was had been kept in a sensory deprivation tank since birth. There were several references to synesthesia (like smelling the color purple).
I would love to find the book again, but can't remember the name. I thought it was called "The Harrowing" but a Google search for that doesn't turn up anything useful.