Many sleep training researchers firmly believe the former. “Don’t underestimate children’s ability to self-regulate,” says Hall, the pediatric sleep researcher who used actigraphy in her study of 235 Canadian families. “Parents can help them learn self-regulation by giving them opportunities to self-regulate. That’s how you look at self-soothing – it’s an opportunity to soothe yourself.”
It’s difficult to objectively measure whether babies are truly calming down or have simply given up calling for help.
One possibility could be measuring cortisol, which is often referred to as the stress hormone. But cortisol rises and falls in response to factors other than stress, and the studies that have measured it have had mixed results. One found that babies’ cortisol levels were elevated immediately after a sleep intervention, but there was no control group of untrained babies to compare it to. The small study of 43 infants found that cortisol decreased, but cortisol was not measured until a week after the intervention. And to find out whether sleep training leads to increased stress over the long term, a third study, Hiscock’s longitudinal study in Australia, sampled cortisol five years later and found no difference between the cohorts.
“Personally, I have a problem with the cortisol studies,” Mindell says. “Cortisol changes throughout the day. Even sampling cortisol is very difficult. It depends on many things, including how many hours a person has been awake, how it’s taken – it’s a complicated thing. People often think, ‘Oh, if we measure cortisol, we’ll know if the baby is stressed or not.
The term “self-soothing” also has a confusing history. Coined by sleep researcher Thomas Anders in the 1970s, it is often used interchangeably with the idea that babies can regulate themselves. For Anders, however, a self-soothing baby was simply one that would go back to sleep without parental intervention — he didn’t attempt to quantify their stress levels.
Of the few studies that have looked at the short- to long-term results of sleep training, none have found an effect on a baby’s attachment or mental health. For example, Hiscock’s study, the largest and longest longitudinal study on sleep training, found that sleep-trained children by age six were no more likely to be insecurely attached to their caregiver than their peers. (Experts like Hiscock say they’re not aware of any studies looking at possible long-term effects of cold turkey cry-it-out, only modified extinction. They also looked at healthy babies who were at least six months old. So this one Results do not necessarily apply to infants who are being trained at younger ages or otherwise.)
Like other longitudinal studies, Hiscock lost contact with a number of families when it came time for the final follow-up: 101 of the original 326. That means it’s theoretically possible that sleep training may have affected some children either negatively or positively over the long term, but their experiences were not recorded. However, it’s more likely that any effects of a single intervention will simply “wash out” after six years, Hiscock says.
The benefits of the reaction
Another way to examine the issue of self-regulation is to look at babies’ developing brains and their limitations. Human babies are born very neurologically immature compared to other mammals, with brains about a third the size of an adult. The prefrontal cortex, the “home” of emotional regulation in the brain, is one of the last parts of the brain to mature, not fully developing until your mid-20s.
As a result, throughout infancy and early childhood, the brain relies on “co-regulation” — the help of a comforting caregiver — to calm itself down. For example, in a position adopted by the American Academy of Pediatrics, the National Scientific Council on the Developing Child defines a “positive” stress response as one resulting from brief, “mild to moderate” stress and “the availability of a caring and responsive adult who helps the child cope with the stressor, providing a protective effect that facilitates the return of stress response systems to baseline”.
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