Understanding the effects of temperament, brain chemistry, and pain sensitivity
© 2009 - 2017 Gwen Dewar, Ph.D., all rights reserved
By definition, colicky babies cry excessively and inconsolably. But why? As I note in
this evidence-based overview of colic, some babies may suffer from specific illnesses, like transient lactose intolerance and gastroesophageal reflux disease.
But there is also evidence that some infants are "wired up" a little differently. They may react differently to care-giving, be more prone to negative emotions, or have a greater sensitivity to pain.
Individual differences of temperament have been observed during the first few days postpartum (Tsuchiya 2011), and to some degree, you can predict which newborns will become colicky by seeing how they respond to being undressed, handled, or put down. The babies who are most upset by these maneuvers are most likely to develop colic (St James-Roberts et al 2003).
So maybe colicky babies are simply less tolerant of disruptions and transitions.
Consistent with this idea, several studies have found that colic symptoms improve when parents are instructed to stimulate their babies less (Lucassen et al 1998).
There's another possibility, too: Colicky babies may also react differently to care-giving maneuvers that are meant to soothe them.
In normally-developing infants, some calming stimuli can trigger the release of endogenous opioids, self-produced painkillers that bathe the brain. Do babies with colic respond the same way?
As noted above, research suggests that colicky babies may have more trouble calming down once they begin crying. In one controlled study, researchers found that normal and colicky babies had the same frequency of crying bouts. What distinguished colicky babies was that they colic cried longer (Barr et al 1992).
This is consistent with the "Pleistocene" baby care experiments that I mention in my review of the research about colicky babies. Increased carrying and breastfeeding reduced crying in normal babies, but not in babies with colic (e.g., Barr et al 1991).
And an experiment with soothing flavors reported similar results. Ronald Barr and colleagues gave 6-week old babies a sugar solution to taste, and discovered that all babies—those with colic and those without—responded to the sugar by calming down.
But the calming effect lasted longer for normal infants. Babies with colic were more likely to resume crying two minutes later (Barr et al 1999).
Why these differences? Barr's team speculates these babies may have a less responsive distress regulation system: Perhaps soothing stimuli are less effective triggers of endogenous opioids (Barr 1999). According to this idea, colic eventually improves because the opioid release system matures.
Then there is a theory based on one of the best-established research findings: Babies with colic are more likely to have higher levels of potentially troublesome bacteria in their digestive tracts, which could make them hypersensitive to pain.
The imbalance of gut flora may activate nerve receptors in the intestines, making babies more sensitive to abdominal pain (Pärtty and Kalliomäki 2017; O'Mahoney et al 2016). If this is the cause of an infant's problems, it's possible that physician-supervised doses of the probiotic bacteria, Lactobacillus reuteri, could help. But the research on this subject is mixed (Pärtty and Kalliomäki 2017).
More studies are needed to understand how probiotics might interact with an individual's pre-existing mix of bacteria (Pärtty and Kalliomäki 2017).
Meanwhile, it seems a good guess that some babies cry excessively and inconsolably because they respond differently to stimulation -- both external and internal.
References: Colicky babies and brain chemistry
Barr RG, McMullan SJ, Spiess H, Leduc DG, Yaremko J, Barfield R,
Francoeur TE, Hunziker UA. 1991b. Carrying as colic "therapy": a
randomized controlled trial. Pediatrics. 87(5):623-30.
Barr RG, Young SN, Wright JH, Gravel R, and Alkawaf R. 1999.
Differential calming responses to sucrose taste in crying infants with
and without colic. Pediatrics. 103(5):e68.
Barr RG, Rotman A, Yaremko J, Leduc D and Francoear TE. 1992. The
crying of infants with colic: A controlled empirical description.
Pediatrics 90: 14-21.Barr 1999
Lucassen PL, Assendelft WJ, Gubbels JW, van Eijk JT, van Geldrop
WJ, Neven AK. 1998. Effectiveness of treatments for infantile colic:
systematic review. BMJ. 316(7144):1563-9.
O'Mahony SM, Dinan TG, Cryan JF. 2016. The gut microbiota as
a key regulator of visceral pain. Pain 58(1):S19–S28.
Pärtty A and Kalliomäki M. 2017. Infant colic is still a
mysterious disorder of the microbiota-gut-brain axis. Acta Paediatr.
St James-Roberts I, Goodwin J, Peter B, Adams D, and Hunt S.
2003. Individual differences in responsivity to a neurobehavioural
examination predict crying patterns of 1-week-old infants at home
Developmental Medicine & Child Neurology 45(6):400-407.
Tsuchiya H. 2011. Emergence of temperament in the neonate:
neonates who cry longer during their first bath still cry longer at
their next bathings. Infant Behav Dev. 34(4):627-31.
content last modified 10/2017
For references cited in my other articles about colic,