It is now clear that genes are turned on and off by environmental influences, including interactions in the nurturing environment, mediated through neurotransmitters and other chemicals. This is called “epigenetic modification.” The quality of environmental stimulation is experienced along a continuum that ranges from growth enhancing to “toxic stress,” defined as “strong and prolonged activation of the body’s stress management systems in the absence of the buffering protection of adult support.” (The Science of Early Childhood Development, 2007, National Scientific Council on the Developing Child)