That childhood sets the stage for our future is a widely-held belief, yet we also know that people can be resilient in the face of hardship. We know that people can make remarkable recoveries; they can “bounce back”. In this post I discuss two main types of interaction between neurological development and the environment that may explain this apparent contradiction:
-An experience-expectant brain development explains the heightened sensitivities to environmental conditions most often occurring during early human development. An example of this is seen in synaptic overproduction during the first 7 years of life, in ‘expectation’ of stimulus and experience, followed by synaptic pruning (Lichtman 2001; Geldart, Mondloch et al. 2002). If an experience-expectant system does not receive the necessary input from the environment during a specific period of development, the brain may develop in an ‘atypical’ way that leads to impairments when processing certain types of information (Watling, Workman et al. 2012).
This form of adaptability links-in with the idea of sensitive periods: ‘During a phase of rapid development, a biological system is more sensitive to exposures in the environment and especially deviations from ‘normal’ exposures ‘expected’ during that particular phase of development for that particular system’ (Bruer 2001). The notion of a single sensitive period is ultimately meaningless. Rather, degrees of sensitivity are constantly shifting for different physiological systems which in turn vary in their complexity. Sensitive periods occur frequently in early life, but continue to happen throughout the life span. Lupien et al schematically refer to the ‘life cycle model of stress’ describing how the effects of stress at different life stages depend upon the brain areas that are developing or declining at the time of exposure (Lupien, McEwen et al. 2009).
-An experience-dependent view, however, explains the physiological adaptability and brain plasticity that humans appear to retain across the lifecourse (Watling, Workman et al. 2012). This form of brain development may reflect fine-tuning or where one skill is be dependent on the development of another skill (Bruer 2001). For example, the ability to process facial emotions requires first that the individual has the ability to perceive the visual input of facial stimuli (Watling, Workman et al. 2012).
Research emphasising the importance of the early childhood environment sometimes comes under fire for being deterministic. Indeed, overly-deterministic views about how early life effects us as adults may be harmful (Yaqub 2002). The way in which we interact with our environment simply shifts from a dominantly ‘experience-expectant’ one early-on characterised by sensitive periods, to a dominantly ‘experience-dependent’ one, where plasticity and the capacity for change is possible. These two broad types of adaptability may be key to understanding how we interact with our environment, and move us away from misnomers such as childhood determinism. Factoring both into our understanding of health may help elucidate how health states occur along socioeconomic gradients.
Simply put, in public health terms, it is never too early and never too late.
PS. Of course, other forms of interaction between individuals and their environments also occur, and are worthy of focus in another blog post…
-Bruer, J. T. (2001). A critical and sensitive period primer. Critical thinking about critical periods. D. B. Bailey Jr, J. T. Bruer, F. J. Symons and J. W. Lichtman. Baltimore, Paul H. Brookes: 299.
-Geldart, S., C. J. Mondloch, et al. (2002). “The effect of early visual deprivation on the development of face processing.” Developmental Science 5(4): 490-501.
-Lichtman, J. W. (2001). Developmental neurobiology overview: synapses, circuits and plasticity. Critical thinking about critical periods. D. B. -Bailey Jr, J. T. Bruer, F. J. Symons and J. W. Lichtman. Baltimore, Paul H. Brookes publishing co.
-Lupien, S. J., B. S. McEwen, et al. (2009). “Effects of stress throughout the lifespan on the brain, behaviour and cognition.” Nature Reviews. Neuroscience 10(6): 434-445.
-Watling, D., L. Workman, et al. (2012). “Emotion lateralisation: Developments throughout the lifespan Introduction.” Laterality 17(4): 389-411.
-Yaqub, S. (2002). “‘Poor children grow into poor adults’: harmful mechanisms or over-deterministic theory?” Journal of International Development 14(8): 1081-1093.