The following essay will define the terms ‘epigenetics’, ‘sensing pathways’ and ‘stress pathways’ and also explain the role they each play in brain development. Epigenetics can be defined as the effect of environmental factors on genes (Palkhivala 2010, p. 5). We are all born with a set of genes which act as a blueprint for development. It is the environmental factors that we experience which alter how, where, when and even if genes are expressed (McCain Mustard & Shanker 2007, p. 20).The study of epigenetics has revealed that our DNA is not our destiny; nurture affects nature (University of California Television 2011). Our genes can be turned on or off dependent on environmental factors, without actually altering our DNA or genetic code (McCain Mustard & Shanker 2007, p. 30). These alterations can be passed on to other generations, with our descendents not only inheriting our genes, but the way they were expressed (McVittie 2008). There are many environmental factors which influence the way our genetic code is read, or which switches are turned on or off (McCain Mustard and Shanker 2007, p. 0). The experiences we have pre and post-natally with nutrition, teratogens (including stress), family and members of the community interact with each person’s genetic potential, influencing not only long term brain function but also our physical and mental health (Rutter 2012; Tremblay 2010, p. 1). The brain is a use-dependent organ which responds to patterned, regular experiences; the more a neural network is activated, the more that part of the brain will change (Ludy-Dobson & Perry 2010, p. 27).Early brain development is particularly vulnerable to the environment be it positive or negative, impacting favourably or not on the processes of neurodevelopment (Perry 2002). The role epigenetics plays in brain development can be exemplified through the lives of identical twins. Identical twins have the same DNA but will encounter different experiences causing differences in gene expression (Mustard 2010, p. 1). Their genetic blueprint is the same but the way it is read is different due to epigenetics leading to differences in behaviour, learning and physical and mental health (Mustard 2010).Epigenetic influences are vital to brain development. Many functions of our brains, including those that relate to sensing pathways such as vision, hearing and touch, expect to receive sensory input for normal development to occur (Berk cited in Carlson 2006, p. 11; Mustard 2006, p. 1). Sensory input accounts for majority of a human’s learning in the first two years of life (Carlson 2006, p. 11) A sensing pathway can be defined as a ‘pathway for impulses for a sensation’ connecting the brain to the body (McCain, Mustard & Shanker 2007 p. 22; Scanlon & Sanders 2010, p. 234).Sensory pathways consist of receptors which detect changes in stimuli; sensory neurons which send this information to the central nervous system and sensory tracts which transmit impulses to specific brain parts (Scanlon & Sanders 2010, p. 34). Sensory stimulation is vital in ensuring neurons form synapses which build strong sensory pathways to support future higher level brain development (McCain, Mustard & Shanker, 2007, p. 22). The importance of timing in relation to sensory input is made clear through studies of the relationship between cognitive development and nurturing care-giving.Observation of Romanian orphans who were not given early experiences through loving two-way interactions such as touch, talking, singing and gazing have shown that this type of emotional and social neglect can have severe life-long consequences on brain development. The Romanian orphan babies are now adults who have brain damage and are unable to meet their own basic needs (Jennings 2005, p. 23). This example demonstrates that ‘an absence of nurturing during the first three years of life can lead to disorganization of neural systems that mediate social-emotional functioning’ (Ludy-Dobson & Perry 2010, p. 2). This line of research also reveals that the social environment we experience during the early years of life can have genetic implications on the formation of stress pathways within the brain (National Scientific Council on the Developing Child 2005, p. 2). Stress pathways can be defined as circuits and hormonal systems which generate reactions to sensory input which is threatening or unfamiliar. Early life experiences which promote a chemical and neural stress response influence the formation of the brain’s adaptive stress pathways (National Scientific Council on the Developing Child 2005).Stress is a normal part of life, and learning to respond to stress is important in healthy development. ‘Positive stress’ which refers to responses which are mild and short in duration and feature the support of positive, caring and safe adult relationships supports normal development (National Scientific Council on the Developing Child 2005, p. 1). Starting preschool for the first time surrounded by warm and nurturing educators is an example of positive stress for a child. Tolerable stress also features the support of caring adults and is short-lived, but involves more serious experiences such as death and divorce.While this type of stress can affect brain architecture, there is the potential for positive effects, dependent on the presence of supportive relationships. When stress is strong, and occurs regularly for a long period of time without the buffer of a caring adult relationship it becomes toxic. Toxic stressors such as neglect, emotional, physical or sexual abuse can cause changes to the architecture of the brain resulting in unhealthy patterns of stress regulation (National Scientific Council on the Developing Child 2010, p. 1).This type of impact can have life-long implications on memory, learning, behaviour, mental and physical health (National Scientific Council on the Developing Child 2005, p. 1; National Scientific Council on the Developing Child 2010, p. 1; Sims, Guilfoyle & Parry 2005, p. 29). On the other hand, ‘positive relational interactions regulate the brain’s stress response systems and help create positive and healing neuroendocrine and neurophysiological states that promote healing and healthy development both for the normal and the maltreated child’ (Ludy-Dobson & Perry 2010, p. 7). In conclusion, our environment and the experiences we are exposed to during our early years of life have profound and lasting effects on the development of our brains. Epigenetics (the environmental effect on genes), stress pathways (circuits and hormonal systems which generate reactions to sensory input which is threatening or unfamiliar) and sensing pathways (pathways which sense impulses connecting the brain to the body) develop dependent upon the types of experiences, their timing and the pattern in which they occur (Ludy-Dobson & Perry 2010, p. 8).