Neglect Harms Infants’ Brains, Researchers Say
Exploring the biology of mother love, researchers reported Monday that parental care makes such a lasting impression on an infant that maternal separation or neglect can profoundly affect the brain’s biochemistry, with lifelong consequences for growth and mental ability.
Children raised without being regularly hugged, caressed or stroked--deprived of the physical reassurance of normal family attention--have abnormally high levels of stress hormones, new research on Romanian orphans raised in state-run wards shows.
Moreover, new animal research reveals that without the attention of a loving caregiver early in life, some of an infant’s brain cells may simply commit suicide. Although the growing brain naturally prunes cells during development--losing up to half by adulthood--the neurons in the neglected animals died at twice the rate of those in animals kept with their mothers.
“What we found shocked us,” said psychologist Mark Smith at the DuPont Merck Research Labs in Wilmington, Del., who analyzed the effects of maternal deprivation in laboratory animals. “Maternal separation caused these cells in the brain to die.
“The effects of maternal deprivation may be much more profound than we had imagined,” he said. “Does this have implications for humans? Frankly, I hope not, but I suspect there may be.”
Scientists have known for decades that maternal deprivation in infancy can mark children for life with serious behavioral problems, leaving them withdrawn, apathetic, slow to learn and prone to chronic illness. But a range of new research, presented Monday in New Orleans at a meeting of the Society for Neuroscience, reveals for the first time the biochemical consequences of emotional neglect on the developing brain.
“It has been known for a long time that early experience is able to shape the brain and behavior,” said Ron de Kloet, an expert on stress and the endocrine system at the University of Leiden in the Netherlands. “Only recently have we been able to go into the brain and measure what is actually happening in early experience.”
It is the relationship between parental care, the neurobiology of touch and the chemistry of stress that lies at the heart of the new insights on how a newborn brain takes shape.
Researchers said that neglect can warp the brain’s developing neural circuits so that they produce too much or too little of the hormones that control responses to stress, causing permanent changes in the way an organism behaves and responds to the world around it. In infants, high levels of stress can impair growth and development of both the brain and the body.
In animal studies, “the presence of the mother ensures these stress hormones remain at a nice low level,” said Michael Meaney of the Douglas Hospital Research Centre in Montreal.
New laboratory research by Meaney and other neuroscientists highlights the long-range biochemical consequences of neglect and the effect of maternal care on the development of brain regions that control responses to stress.
Studies with laboratory animals show that the simple act of a mother licking her pup triggers a surprisingly subtle chain of biochemical events inside the infant’s brain. As the mother physically comforts her newborn, it stimulates the production of key biochemicals that inhibit production of a master stress hormone called CRH.
An infant’s budding nervous system is so attuned to the reassurance of a gentle, stroking touch that researchers were easily able to protect newborn mice from the most destructive biochemical effects of the stress of maternal deprivation. They simply whisked them softly with a moist paintbrush for less than a minute three times a day, de Kloet reported Monday.
“The results demonstrated that one of the critical aspects of maternal behavior is the tactile contact between mother and infants,” de Kloet said. “Stroking was able to almost completely reverse the endocrine and brain changes that are seen following maternal deprivation.”
To determine whether these new laboratory insights also apply to human child-rearing, researchers are now assessing the changing brain chemistry of children and the attention they receive from their primary caregiver, be it mother, father or day-care worker.
In work presented Monday, Harvard University researchers who studied Romanian infants raised in orphanages reported that when lacking the attention and stimulation typical of family life, the 2- to 3-year-old children developed abnormally high and lasting levels of the stress hormone cortisol, which can have serious long-range effects on learning and memory.
Mary Carlson, the Harvard Medical School scientist who studied the children, also discovered that youngsters whose families kept them in poor-quality day-care centers on work days had abnormal levels of stress hormones on weekdays but not on the weekend when the children were home.
The children who had the highest levels of cortisol also had the lowest scores on tests of mental and motor ability. Abnormal levels of cortisol can cause changes in the hippocampus, a structure in the brain involved in learning and memory.
“Our findings support clinical research showing that infants cared for in institutions grow slowly and have behavioral retardation,” Carlson said.
