Babies sometimes overhear our heated arguments. Does it matter? A new study suggests that it does. When researchers played recordings of angry voices to sleeping babies, they found that the babies’ home life predicted a specific brain response: Babies from high-conflict homes experienced more activity in parts of the brain associated with stress reactivity and emotion.
The study targeted 20 babies between the ages of 6 and 12 months, and depended on mothers’ reports about how much parents argued at home. To measure brain activity, the babies were put in functional MRI scanners while they slept. And while the scan was in process, each baby heard a variety of audio playbacks.
All playbacks featured the voice of a man speaking a series of nonsense words. But in some trials, the voice sounded happy. In others, the voice sounded very angry. There were also trials where the voice spoke in neutral tones.
When the researchers compared brain activity in response to the angry and neutral voices, they found a link with reported levels of non-physical conflict between parents. Babies from higher-conflict homes showed more activity in a part of the brain called the rostral anterior cingulated cortex, or rostral ACC, a region associated with the processing of emotion.
There was also increased activity in more primitive parts of the brain, including the hypothalamus, a structure that controls and directs the stress response.
This pattern was not evident when researchers compared reactions to the happy and neutral voices.
The results seem telling. Previous studies have established that early-life adversity is linked with subsequent emotional problems and stress-related disease. The rostral ACC is frequently altered in people suffering from stress disorders. And higher levels of conflict between parents have been linked with greater stress reactivity – or more sluggish recovery from stress – in infants.
So perhaps this study offers a window on how it all begins. Exposure to angry voices – even during sleep – puts a baby’s emotional circuits in overdrive.
And what’s especially notable about this research is that it focused on moderate sources of stress. We already know that the terrible stuff – abuse and neglect – is linked with lasting changes in the brain and stress response system. This study suggests that less extreme stress may also leave a mark.
Can we be sure the key difference between babies was overhearing angry arguments at home? Maybe not.
The mothers in this study were volunteers who responded to a Craigslist ad, not patients under referral for psychological problems. So we have no special reason to think they suffered from any special pathology. And the researchers screened the families for involvement with child welfare services, which helps rule out the possibility that infants were exposed to more than non-physical partner conflict at home. But the study didn’t control for maternal stress during pregnancy, and I wonder if the results reflect, at least in part, the effects of the mother’s stressful home life on the developing fetus. There is also the ever-present question about heredity. Do the kids of stressed-out mothers inherit genes that make them more reactive?
But “adoption” experiments on rats suggest that the environment trumps genetics when it comes to the development of the stress response system. And in any event, this study tells us that some babies have a special sensitivity to the sound of anger, and they don’t have to be awake for their brains to react. When we dismiss the possibility that our babies are adversely affected by our grown-up battles, we are kidding ourselves.
If your baby has been exposed to stressful conditions – before or after birth – there is a lot you can do to help. Research suggests that frequent, affectionate touch can reverse the effects of prenatal stress. And warm, sensitive, responsive parenting appears to buffer kids from the negative effects of growing up in stressful environments. Check out these links, as well as my articles, “Everyday stress in babies: What research suggests about keeping babies calm and happy,” and “Difficult babies can become super kids” for more information.
Reference: Graham AM, Fisher PA, and Pfiefer JH. 2013. What sleeping babies hear: A functional MRI study of interparental conflict and infants’ emotion processing. Psychological Science. In press.
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