Holding hands with a loved one might spark more of a connection than just the feeling of flesh on flesh: new research suggests it causes our breathing and heart rates to sync up between partners, and could even ease bodily pain.
That's the conclusion based on a study of 22 couples, a study which adds to a growing body of research on interpersonal synchronisation.
It turns out that there are actually plenty of ways our bodies automatically slide into sync with each other.
In this case the experiment was prompted by a real-world event: lead researcher Pavel Goldstein, from the University of Colorado Boulder, found that when he held his wife's hand during the birth of their daughter, her labour pains eased off.
"I wanted to test it out in the lab," says Goldstein. "Can one really decrease pain with touch, and if so, how?"
The 22 heterosexual couples enlisted for the study were aged 23 to 32 and had been together for at least a year. While their brain waves were monitored through the use of electroencephalography (EEG) caps, they were put through a series of scenarios.
These scenarios included sitting together and not touching, sitting together holding hands, and sitting in separate rooms. Each different scene was repeated while mild heat pain was applied to the arm of the woman in the couple.
When the partners were in the same room, whether or not they were touching, the researchers noted some brain wave synchronicity in the alpha mu band – a wavelength associated with focused attention.
This sync was strongest when the pair were holding hands and the woman was in pain.
On those occasions when the woman was in pain and the couple couldn't hold hands, the brain wave syncing decreased. It seems touch is important in easing pain – just sitting together isn't enough.
"It appears that pain totally interrupts this interpersonal synchronisation between couples and touch brings it back," says Goldstein.
What's more, when the male partner felt more empathetic to his partner's pain, the brain activity syncing increased, and the more the pain was reduced.
While it's not immediately clear why that would be – we'll need a lot more studies like this to find out – it's possible that when we feel like someone is sharing our pain, that helps the brain manage it better.
This is actually the second paper to be published on this experiment, and it backs up the findings of the first, where touch was shown to reduce pain and put heart rate and breathing rates in sync between partners.
The newly published findings add details on the brain wave monitoring that was carried out during the tests. While the research doesn't use a huge sample size, it's large enough to suggest something is triggered in our biological systems when we hold hands.
It's far from the only study to reach this kind of conclusion either. Last year a study found that conversing with a partner, even if we don't know them, causes oscillations in brain activity to start to match up.
Perhaps there's something deep in our wiring that means we seek out companionship and are trained to get in sync with other people, even on a subconscious level.
This syncing is something that happens in physics too, though scientists aren't completely sure why.
Considering the new study didn't look at same-sex relationships or indeed any other type of relationship – like father and son – we wouldn't recommend grabbing the hands of random strangers on the bus.
But in the delivery room scenario that sparked off the research, some hand-holding could really help.
"We have developed a lot of ways to communicate in the modern world and we have fewer physical interactions," says Goldstein.
"This paper illustrates the power and importance of human touch."
The latest research has been published in PNAS.