Pre-term babies spend 15 minutes of their first days on Earth hiccuping – the most of any human – and it’s these 15 minutes that scientists now believe could answer the age-old question: Why do we hiccup, and to what purpose?
Humans start hiccuping at nine weeks’ gestation, a habit that carries through to when a child is born.
We’re more likely, pre-term or not, to hiccup when we’re young.
This frequency that fades away with age (although doesn’t completely disappear, as any adult who has lived through a hiccup attack can relate to) could very well point to hiccups being a key part in our developmental pathways.
New research from UCL this week shows a link between the action and brain waves that remind a baby’s body to breathe, which leads to a natural reflex to adapt a breathing pattern.
Study lead author Kimberley Whitehead said this finding led the team to believe hiccups just stuck around in later life, as a hangover from infancy.
“The reasons for why we hiccup are not entirely clear, but there may be a developmental reason, given that fetuses and newborn babies hiccup so frequently,” Ms Whitehead said.
How the hiccup was solved
To reach these conclusions, the UCL team studied 13 newborn infants (from 30 to 42 weeks gestational age) who were experiencing bouts of hiccups.
Simultaneously, they recorded their brain activity through electrodes on the scalp, while movement sensors monitored the infants’ torsos to detect when they were hiccuping.
They found when the baby hiccuped, it triggered three large brainwaves.
It was the third one that held the most interest for them: It worked in the same way that a brain reacts to sound. So the “hic” onomatopoeia of the movement created a development link between diaphragm contractions and breathing.
Study senior author Dr Lorenzo Fabrizi explained: “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 voluntary 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.”
This discovery means hiccups might fall into the category of vestigial reflexes – something that a species still experiences that once had an important purpose, but is now defunct and unnecessary.
In humans, these reflexes still exist.
There’s goosebumps, which used to raise the hair or fur on our skin to protect us against the cold. Or, if we were faced with a threat, to make us appear bigger and scarier to our foe.
Have you ever had your arm or leg jerk suddenly, while you’re on the verge of falling asleep?
That’s called the hypnic jerk, and it probably stems from way, way back, when humans used to sleep in trees.
Science isn’t 100 per cent sold on the origin of the jerk, but the tree sleeping root makes sense: You’d be pulled from your sleep just to definitely make sure you were in a stable position and not at risk of falling out.