A sweet pill to swallow : New studies show the placebo effect at work from head to toe in different cultures around the world. Using new techniques of brain imagery, they are uncovering a host of biological mechanisms that can turn a thought, belief or desire into an agent of change in cells, tissues ad organs. They are also learning that much of human perception is based not on information flowing into the brain from the outside world but what the brain, based on previous experience, expects to happen next.