November 14, 2019
Hiccups are a nuisance, especially when they show up at an embarrassing moment, or they won't dissipate easily. But the reason they happen has been something of a mystery.
A new study from the University College London suggests that as newborn babies our hiccups help the brain learn to regulate breathing.
In the study, published in the journal Clinical Neurophysiology, researchers used brain scans of newborn infants to better understand why fetuses and newborn babies hiccup so much. Fetuses start to experience hiccups as early as nine weeks gestational age and pre-term infants spends about 1% of their day hiccuping.
"A hiccup occurs when the brain sends a signal for the diaphragm to shift forcefully downward, suddenly pulling a lot of air into the back of the throat," Harvard Health explains. The 'hic' sound of the hiccup is caused by a part of the throat closing temporarily.
"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," the study's senior author, Dr. Lorenzo Fabrizi said in a statement.
"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."
Researchers included 13 newborn infants in the study. Some of the babies were full-term while others pre-term. Gestational ages ranged from 30 to 42 weeks.
They used electroencephalography (EEG) electrodes on the top of the head and movement sensors on the upper body to analyze the relationship between brain activity and hiccups.
When the diaphragm muscle contracted during a hiccup, there were three corresponding large brainwaves, researchers found. The third brainwave makes the connection between the sound of the hiccup and the movement of the diaphragm. All the hiccups occurred while the babies were either awake or engaged in active sleep.
"The muscle contraction of a hiccup is quite big – it's good for the developing brain because it suddenly gives a big boost of input, which helps the brain cells to all link together for representing that particular body part," Research Associate Kimberly Whitehead, the study's lead author told CNN.
She added, "Our findings have prompted us to wonder whether hiccups in adults, which appear to be mainly a nuisance, may in fact [be] a vestigial reflex, left over from infancy when it had an important function."