Although we know how we hiccup, why has remained a mystery for some time, with researchers suggesting it to be an evolutionary hangover from when our ancestors had gills and lived in the sea (Snow: 2012). Now however, a new study from University College London (UCL) has found a biological purpose the function: when newborn babies hiccup, certain brain waves are triggered that help them regulate their breathing.
Unborn children begin to hiccup in the womb at just nine weeks old, making them one of the earliest patterns of human activity. In particular however, children born before 37 weeks of gestation, known as preterm infants, are especially prone to hiccuping, spending an estimated 1% of their time in the act; equal to 15 minutes per day.
According to Kimberley Whitehead, the lead author of a study uncovering why newborn infants hiccup, “The reasons for why we hiccup are not entirely clear, but there may be a developmental reason, given that foetuses and newborn babies hiccup so frequently (University College London: 2019).”
For the study, researchers studied 13 newborn infants in a neonatal ward who frequently hiccupped. Ranging from 30 to 42 weeks gestational age, the researchers selected a mix of preterm and full-term babies in an attempt to reflect typical natal development within the last trimester of pregnancy.
Previously, the same researchers had found that babies may kick in the womb to develop mental maps of their own bodies. Thus, they suspected that hiccuping may serve a similar mechanism- rather than mapping the external body however; mapping the internal.
To establish this, they recorded the babies’ brain activity with electroencephalography (EEG) electrodes on their scalps, alongside movement sensors placed on their torsos to gather a linked record of when they were hiccuping.
When looking at their results, they found that the contractions by the diaphragm muscle from their hiccups led to the simultaneous release of two large brainwaves, followed by a third. As the third of these was similar to that stimulated by a noise, they hypothesized that a newborn baby’s brain may be able to associate the “hic” sound of the hiccup to the feeling of their diaphragm muscle contracting, and thus be better able to regulate their breathing.
Dr Lorenzo Fabrizi, the study’s senior author, said, “The activity resulting from a hiccup may be helping the baby’s brain to learn how to monitor the breathing muscles so that eventually breathing can be voluntarily controlled by moving the diaphragm up and down...When we are born, the circuits which process body sensations are not fully developed, so the establishment of such networks is a crucial developmental milestone for newborns.”
Thus, the researchers suggested that hiccups in adults may indeed just be a vestigial reflex left over from early childhood when it served a function.
Snow, John B.: Live Science