Hidden switches in the mind.

Mental illness is not due to mutations in a single gene, but rather involves molecular disturbances entailing multiple genes and numerous environmental factors that control their expression. Recent research has demonstrated that complex “epigenetic” mechanisms, which regulate gene activity without altering the DNA code, exert long-lasting effects within mature nerve cells. This review summarizes recent evidence for the existence of sustained epigenetic mechanisms of gene regulation in nerve cells that have been implicated in the long-lasting regulation of complex behavior, including behavioral abnormalities in several psychiatric disorders such drug addiction and depression. We also critique recent and still uncertain evidence that similar epigenetic changes, occurring in germ cells, might mediate the trans-generational transmission of behavioral experience and, possibly, mental illness.