An epigenetic mechanism refers to any hereditary influence (in the progeny of cells or individuals) on the function of chromosomes or genes that is not accompanied by a change in the DNA sequence (Yoder et al 1997). ; a change in phenotype without a change in genotype. These changes can persist over several generations of cell divisions. Although it was once thought that there was no new generation of neurons in the nervous system, studies have shown that the brain retains neural stem cells (NSCs) into adulthood and that neurogenesis continues to happen. Neural stem cells (NSCs) are the first cells found in the nervous system and differentiate into the main cell types: oligodendrocytes, astrocytes, and neurons. There are three epigenetic mechanisms that are involved in each of these differentiations; these are DNA methylation, histone modifications and non-coding ribonucleic acid (ncRNA) expression, which lead to the correct genes being turned on and off at each stage. Epigenetic mechanisms have been implicated in several functions of the nervous system, such as neurogenesis, neuronal-glial differentiation, and also play a role in higher functions such as memory and cognition. A major mechanism in epigenetics is DNA methylation. DNA methylation occurs by two mechanisms and involves the addition of a methyl group (-CH₃) via covalent bonding to a cytosine side chain. DNA methylation is catalyzed by a group of enzymes called DNA methyltransferases (DNMTs). DNMT adds methyl groups to cytosine residues. Cytosines must be immediately followed by a guanine. Because they are methylated, they are called CpG dinucleotides. About 70% of these dinucleotides are methylated while the rest are grouped into clusters called CpG islands. There are two types... middle of article......Glass, Non-coding RNAs as regulators of gene expression and epigenetics, 2011, Oxford Journals, 90 (3), p430- 440J. David Sweatt. (2009). Experience-dependent epigenetic modifications in the CNS. Biol Psychiatry. 65 (3), 191-197. Chwang WB, O'Riordan KJ, Levenson JM, Sweatt JD. ERK/MAPK regulates hippocampal histone phosphorylation following contextual fear conditioning. Learn Mem. 2006;13:322–328Kaili Anier, Anti Kalda, epigenetics of the nervous system. Learn Mem. 2006; 43-72Atd Bio, Epigenetics, 2013,Feng. J. Chang, H. Li E., Fan G. Dynamic expression of de novo DNA methyltransferases DNMT3a and DNMT3b in the central nervous system. J Neruoscience Res, 2006 (79), p734-746 Korzus E, Rosenfeld MG, Mayford M. Histone acetyltransferase CBP activity is an essential component of memory consolidation. Neuron 2004;42:961-72