Behavioral epigenetics is the field of study examining the role of epigenetics in shaping animal (including human) behaviour. Epigenetic gene regulation involves changes other than to the sequence of DNA and includes changes to histones (proteins around which DNA is wrapped) and DNA methylation. These epigenetic changes can influence the growth of neurons in the developing brain as well as modify activity of the neurons in the adult brain. Together, these epigenetic changes on neuron structure and function can have a marked influence on an organism's behavior.
The first documented example of epigenetics affecting behavior was provided by Meaney and Szyf. While working at McGill University in Montréal in 2004, they discovered that the type of mothering a rat receives in infancy determines how that rat responds to stress later in life. Rat pups that receive a less nurturing upbringing are more sensitive to stress throughout their life-span. This stress sensitivity is linked to a down-regulation in the expression of the glucocorticoid receptor in the brain. In turn, this down-regulation was found to be a consequence of the extent of methylation in the promoter region of the glucocorticoid receptor gene. This pioneering work in rodents has been hard to replicate in humans because of a general lack of human brain tissue for measurement of epigenetic changes. The first study that has directly linked epigenetic changes in human brain tissue to behavior involved post-mortem brains of people who committed suicide, half of whom had been abused as children. Those who had been abused had a lower expression of glucocorticoid receptor due to increased methylation in the promoter region of the glucocorticoid receptor gene. These observations in humans closely parallel the earlier rat studies.
Histone modification 
Histone modification has a strong effect on transcriptional regulation. Furthermore synaptic plasticity and long-term memory are dependent on transcription. One factor that has been shown to critical to synaptic plasticity and the formation of long-term memory is the transcriptional coactivator CREB-binding protein which has histone acetyltransferase (HAT) activity.
DNA methylation 
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