Childhood Experience and the Expression of Genetic Potential: What Childhood Neglect Tells Us About Nature and Nurture
These findings strongly suggest that when early life neglect is characterized by decreased sensory input (e.g., relative poverty of words, touch and social interactions) there will be a similar effect on human brain growth as in other mammalian species. The human cortex grows in size, develops complexity, makes synaptic connections and modifies as a function of the quality and quantity of sensory experience. Sensory-motor and cognitive deprivation leads to underdevelopment of the cortex in rats, non-human primates and humans.
Figure 1. Abnormal brain development following sensory neglect in early childhood. These images illustrate the negative impact of neglect on the developing brain. In the CT scan on the left is an image from a healthy three year old with an average head size (50th percentile). The image on the right is from a three year old child suffering from severe sensory-deprivation neglect. This child's brain is significantly smaller than average (3rd percentile) and has enlarged ventricles and cortical atrophy.
Studies from other groups are beginning to report similar altered neurodevelopment in neglected children. In the study of Romanian orphans described above, the 38% had FOC values below the third percentile (greater than 2 SD from the norm) at the time of adoption. In the group adopted after six months, fewer than 3% and the group adopted after six months 13% had persistently low FOCs four years later (Rutter et al., 1998[41]; O'Connor et al., 2000[25]). Strathearn (submitted[45]) has followed extremely low birth weight infants and shown that when these infants end up in neglectful homes they have a significantly smaller head circumference at 2 and 4 years, but not at birth. This is despite having no significant difference in other growth parameters.
More recently advanced neuroimaging techniques have demonstrated altered brain development in neglected children. Chugani and colleagues have been pioneers in neuroimaging studies in maltreated children. Their most recent study using functional MRI in Romanian orphans has demonstrated decreased metabolic activity in the orbital frontal gyrus, the infralimbic prefrontal cortex, the amygdala and head of the hippocampus, the lateral temporal cortex and in the brainstem (Chugani et al., 2001[3]). Together these findings suggest a global set of abnormalities matched by the functional abnormalities in cognitive, emotional, behavioral and social functioning.
Figure 2. Sensory deprivation neglect: effects of early removal on recovery. Children were removed from neglectful environments at different ages (ages 8 months to 5.7 years). Their frontal-occipital circumference was measured and compared to same-aged norms (blue bars). Children were placed in foster care and one year later re-evaluated. FOC was measured (maroon bars) and in each group increased although with increasing age, the improvement after a year of foster placement started to decrease such that children removed after four years in the neglectful setting had no statistically-significant improvement one year later. Data are from 112 children with some form of severe neglect in the first five years of life (modified from Perry and Pollard, 1997[30]).
EMOTIONAL NEGLECT IN EARLY CHILDHOOD: THE UNDER-EXPRESSION OF SOCIO-EMOTIONAL POTENTIAL
Clinical attention has been focused on extremes of neglect. The obvious clinical syndromes which result from pervasive neglect have facilitated research in this area. More recently, however, many researchers have observed and studied abnormalities in the capacity of children — and adults — to form healthy relationships. An emerging area of study is focusing on "attachment" — a special form of emotional bond. While usually not framed in context of developmental neglect, attachment problems in children often are the result of mistimed, abnormal or absent caregiving interactions and, therefore, may represent a special case of neglect. As with other brain-mediated capabilities, the capacity to form relationships results from the experience-based expression of an underlying genetic potential to create the neural systems mediating socio-emotional behaviors.
At birth an infant has yet to form a true relational bond with another person. In most instances, the infant will be cared for by an attentive, attuned and loving caregiver.When this happens, a caregiver will, again and again, come to the hungry or cold or scared infant. Warming, soothing, feeding, cleaning and calming the infant, the caregiver creates a set of specific sensory stimuli which are translated into specific neural activations in areas of the developing brain destined to become responsible for socio-emotional communication and bonding. The somatosensory bath — the smells, sights, sounds, tastes and touch — of the loving caregiver provides the repetitive sensory cues necessary to express the genetic potential in this infant to form and maintain healthy relationships. This first and most primary of all relationships is this attachment bond.
