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March 05, 2007
Studies Show How Stress Damages Young Brains
Research in the past has suggested that people who are genetically or biologically predisposed to schizophrenia and other mental illnesses are more sensitive to stress in their family and broader social environment. (see research here, here and here - and social isolation also causes significant stress for children). This area of research on how environment affects genes is called epigenetics, and we've covered this topic in the past here.
This past week there have been two studies published that suggest how stress may damage the brains of young children.
The first study is based on new research from the Child Development Laboratory at the University of Maryland shows that shyness (also called "social anxiety" by psychologists) in children seems to be triggered when a stress-related gene in children interacts with being raised by stressed-out parents. In this study the research focused on how moderate levels of parental stress (i.e. work related, or interpersonal stress) impacted child development.
In the study (published in the February issue of Current Directions in Psychological Science), Nathan Fox, professor and director of the Child Development Laboratory, and his team found that kids who are consistently shy while growing up are particularly likely to be raised by stressed-out parents, and to possess a genetic variant associated with stress sensitivity.
This suggests that shyness is caused by interactions between genes and the environment, as opposed to either genes or the environment acting alone. "Moms who report being stressed are likely to act differently toward their child than moms who report little stress," said Fox. "A mom under stress transfers that stress to the child. However, each child reacts to that stress somewhat differently. The study found that genes play a role in this variability, such that those children who have a stress-sensitive variant of a serotonin-related gene are particularly likely to appear shy while growing up when they also are raised by mothers with high levels of stress.
"We don't understand how the environment directly affects the gene, but we know that the gene shows particularly strong relationships to behavior in certain environments." Dr. Fox suggested.
Like all genes, the particular serotonin-related gene examined in this study has 2 alleles (alleles are the different versions of the same gene - with slight differences), which can be long or short. The protein produced by the short form of the gene is known to predispose towards some forms of stress sensitivity.
Fox's research found that among children exposed to a mother's stress, it was only those who also inherited the short forms of the gene who showed consistently shy behavior.
"If you have two short alleles of this serotonin gene, but your mom is not stressed, you will be no more shy than your peers as a school age child," says Fox. "But we found that when stress enters the picture, the gene starts to show a strong relationship to the child's behavior," says Fox. "If you are raised in a stressful environment, and you inherit the short form of the gene, there is a higher likelihood that you will be fearful, anxious or depressed." Additional research suggests that shy people are also at a significantly higher risk for anxiety disorders, clinical depression and suicide if they experience high levels of stress later in life, however, research also suggests that psychological therapy can reduce this risk of anxiety, depression and suicide for people who are shy.
This research on social anxiety / shyness also ties into the latest theories on social epigenetics, parenting and children's mental health. Researchers are now recognizing that parenting approaches that are highly attuned to the child's state of mind, and which are sensitive to the child's fears and stresses, shows empathy towards the fears, and seeks to lower those anxieties by educating the child about positive responses to the fears - are parenting approaches that seem to result in the children with the lowest risk of mental illness. See these links for more information here and here.
Although similar effects have been seen in animal studies, this is the first time the findings have been replicated in children. The researchers focused on kids in extreme situations to better understand how stress affects brain development.
"We're not talking about the stress of doing your homework or fighting with your dad," said Packard Children's child psychiatrist Victor Carrion, MD. "We're talking about traumatic stress. These kids feel like they're stuck in the middle of a street with a truck barreling down at them."
Carrion, assistant professor of child and adolescent psychiatry at the medical school and director of Stanford's early life stress research program, and his collaborators speculate that cognitive deficits arising from stress hormones interfere with psychiatric therapy and prolong symptoms.
The children in the study were suffering from post-traumatic stress disorder, or PTSD, as a result of undergoing physical, emotional or sexual abuse, witnessing violence or experiencing lasting separation and loss. This type of developmental trauma often impairs the child's ability to reach social, emotional and academic milestones.
"We'd really like to understand why some children are more resilient than others, and what the long-term effects of extreme stress are," said Carrion, who is the first author of the research, to be published in the March issue of Pediatrics. "We know, for example, that these children are at higher risk of developing depression and/or anxiety as adults."
One theory posits that everyone carries an ongoing stress burden that accumulates throughout life. Once a certain threshold is reached, either through one or two very traumatic events or through chronic, high levels of stress, adults and children can begin to exhibit PTSD symptoms such as re-experience (including flashbacks, intrusive thoughts or nightmares), avoidance and emotional numbing, and physiological hyperarousal (such as an elevated resting heart rate). These behavioral symptoms make PTSD difficult to differentiate from other conditions such as attention deficit/hyperactivity disorder.
Children predisposed by genetics or environment to be more anxious than their peers are also more likely to develop PTSD in response to emotional trauma, perhaps because their responses to other life experiences simply left them closer to that threshold than less-anxious children.
The researchers studied 15 children from ages 7 to 13 suffering from PTSD. They measured the volume of the hippocampus at the beginning and end of the 12- to 18-month study period. After correcting for gender and for physiological maturity, they found that kids with more severe PTSD symptoms and higher bedtime cortisol levels (another marker of stress) at the start of the study were more likely to have reductions in their hippocampal volumes at the end of the study than their less-affected, but still traumatized peers.
It is significant that the change in the hippocampal volume corresponds to both PTSD symptom severity and increased cortisol levels. Cortisol belongs to a class of human hormones known as glucocorticoids that have been shown to kill hippocampal cells in animals. In a vicious cycle, a reduction in hippocampal size can make it more difficult for a child to process and deal with traumatic events, which in turn may raise both stress and cortisol levels that cause even more damage.
"Although everyday levels of stress are necessary to stimulate normal brain development, excess levels can be harmful," said Carrion, likening the biological effects of increasing amounts of stress to an inverted U. "One common treatment for PTSD is to help a sufferer develop a narrative of the traumatic experience. But if the stress of the event is affecting areas of the brain responsible for processing information and incorporating it into a story, that treatment may not be as effective."
Carrion and his colleagues are now using an imaging technique known as functional MRI to visualize whether and how the children's brains differ when performing emotional and cognitive tasks.
"What we have now is basically a snapshot," said Carrion. "We can't yet say much about function. But we know that PTSD is chronic and pervasive. Hopefully with further research we can develop more effective, targeted interventions to help these kids."
The study was funded by the National Institutes of Health, the National Alliance for Research on Schizophrenia and Depression, the American Foundation for Suicide Prevention and the Aloha Foundation.
Other co-authors include professor of psychiatry Allan Reiss, MD, and former postdoctoral scholar Carl Weems, PhD, who is now an associate professor of psychology at the University of New Orleans.
Related Story: Stress may 'damage child brains' (BBC)
Related Research Papers:
Current Directions in Psychological Science (the research paper cited in the first news story does not yet seem to be available online).
Posted by szadmin at March 5, 2007 09:02 AM
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