Different classifications of stimuli up-regulate and down-regulate genes. We activate experience-dependent genes, for example, by doing new things or learning new information. These genes are responsible for stem cells getting the instructions to differentiate, transforming into whatever type of cell the body needs at that particular time to replace cells that are damaged. We activate behavioral state–dependent genes when we are in high levels of stress or arousal, or in alternate states of awareness, like dreaming.
