Stages, Challenges and Milestones

Sensitive Periods

Classic psychological theory, of the kind many of us learned in college, favors the idea that humans progress through stages of development. Freud proposed the oral, anal, phallic, and latency periods of childhood which conformed with his ideas about psychodynamic processes. Erikson proposed that in their first year, infants develop trust (or mistrust), in the second year autonomy (or shame and doubt), in the preschool years initiative (or guilt), and later industry, identity, intimacy, generativity and integrity (Smith, Cowie, & Blades, 2003). Later Piaget emphasized cognitive development and proposed the sensorimotor, preoperational , concrete operational, and formal operational stages which described styles of thinking and reasoning (Smith et al., 2003).

Recent authors have focused on more specific physical and cognitive abilities and on “sensitive periods” in human ontogeny linked to these skills. A sensitive period is a short time period, usually taking place in the early life course but sometimes later, during which certain environmental input is required for development to proceed normally. This term is now favored over the earlier term, “critical periods,” because of the modern understanding that problems arising during these periods are sometimes reversible. In the visual, auditory, olfactory, and somatosensory systems, “... it is well established that ... development is somehow conditional to the presence of specific experiential stimulation at definite times during ontogeny” (Gendreau & Lewis, 2005, p. 52). A familiar example is the work done by Conrad Lorenz who famously demonstrated a critical period for “imprinting” among precocial birds, who followed pairs of distinctively marked yellow boots because those were the first moving object they saw in the hours after hatching (cited in Gendreau & Lewis, 2005).

Early writers about delinquents believed that significant early deprivations were important in the etiology of antisocial behavior. In his early career, Bowlby (1944) observed that many of the thieves he encountered in his clinical work had experienced a separation from parents of 6 months or more before age 5. Together, these imply a sensitive period for maternal contact in young humans.

It is important to understand, when considering “sensitive periods,” that research on brain plasticity suggests that the developmental process may be subtractive, beginning with an overproduction of synapses in early development, and proceeding via “selective preservation” and the loss of unused synapses (Lerner, 1984). For our purposes in understanding aggression, research on possible sensitive periods in the development of social behavior is of interest. To date, there has not been a great deal of research directly related to this issue, but two areas have been examined in many studies: maternal deprivation and social isolation.

If brain plasticity in early life is characterized by the loss of unused brain connectivity after an initial overproduction of synapses as proposed (Greenough, Black, & Wallace, 1987), it follows that early maternal deprivation and social deprivation may cause the brain to “lose” important connections related to emotional and social behavior development. The occurrence of such deprivation very early in life may impede fundamental processes needed to establish the architecture for future social behavior. So we might easily expect that severe neglect, characterized by stimulation deprivation, would result in the child victim failing to acquire an important knowledge base for his future functioning. In addition, however, a sensitive period, coupled with the fact of subtractive neurological development, would imply that he would also lose much of his capacity to learn about important aspects of the environment, relationships, and objects (more on maternal deprivation below).

It should be noted that early problems in “sensitive periods” are not always permanent. Research on enriched environments shows that brain development responds significantly to enhanced environmental stimuli, and sensitive periods can be extended (Gendreau & Lewis, 2005). Even adult nervous systems continue to develop, mainly by increasing dendritic connections in response to experience (Greenough et al., 1987) and the myelination of axons.

In general, studies of “timing” of various criminogenic factors imply but do not explicitly test “sensitive periods.” But such studies do suggest that timing in the broader sense matters because the causal factor in question, such as child abuse or exposure to delinquent peers, matters more at some stages in life than others within the culture being studied. Other areas that might be worth looking at are the development of moral values, which usually begins around the age of 2 (Rutter, 1994), and language skills and EFs, which are acquired early and which have been associated with criminality. Later in this chapter, we will return to this topic in a discussion of attachment, parental warmth, and abuse.


Another view of sensitive periods is presented in the “programming model” (O’Connor, 2006). In the sensitive period model, there is a critical period in the ontogeny of an organism during which environmental input is needed for development to proceed. The programming model suggests that adaptations occur during sensitive periods wherein the biological processes of the fetus and child adapt to their environment (O’Connor, 2006). These adaptations are thought to “set” the system, and the setting persists into adulthood. For example, exposing a fetus to stress may cause changes in the way the developing child will respond to stress in his future life outside the womb. Field (2007) describes numerous lines of research on infants that are consistent with the programming model. Research has shown that maternal stress during pregnancy, including daily hassles, depression, anxiety, and anger, stimulate stress hormones and excessive activity in the fetus. High cortisol and low dopamine levels in angry mothers have been mimicked by their newborns. Disruptions in early caregiving appear to have long-term effects on the hypothalamic-pituitary-adrenal (HPA) axis which mediates cortisol (stress) response. These examples suggest that maternal emotion and stress during pregnancy and environmental experiences after birth may affect the functioning of the child’s neurophysiological stress system.

For our purposes, there are no applications directly associated with delinquency. We might speculate, however, that some of the factors associated with criminality, such as child abuse or neglect, poverty, parenting factors and the like, may exert effects in part by this type of programming very early in life. For example, poor nutrition or high stress associated with poverty, abuse, neglect, and family conflict may cue the infant to release more stress hormones, or fewer, in response to problems. This may later “set the table” for angry or hyperactive or overly aggressive responding in some social situations that may translate into physical aggression or violence, given other necessary circumstances.

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