stem cells are specialized cells that have the ability to become any type human cell. Stem cells are NOT brain cells. When the sperm fertilzes the egg and the egg begins to divy up those first building blocks are stem cells. They could become any type of human tissue (maybe not red bloods cells, they're kinda differant). The idea is that if somebody has a spinal cord injury (like christopher reeve) stem cells could be transformed in to new spinal cord cells. This applies to any damaged cells a person may have that the human body can't naturally regenerate (ie: neurons in the brain). Stem cell research could bring many groundbreaking new cures to diseases. The main debate surrounding them though is that pro-life types beleive that using a fertilized egg for research is murder. I don't personally agree, but what ever to each his own I guess