Holding your breath and diving into a pool of cold water might sound like an uncomfortable experience, but biologist John Campbell says it triggers a reflex that leaves animals feeling surprisingly calm.
“This is something we study in the lab, not in people but in mice, and I think what’s happening is it’s engaging this really powerful reflex that we all have – all mammals basically – called the diving reflex. It causes your heart rate to dramatically decrease. It’s a survival reflex – something that’s meant to keep us alive by allowing us to stay under water for a longer period of time," he explains.
In truth, he adds, you don’t have to dive, and the water doesn’t have to be cold.
“Colder water seems to have a stronger effect engaging the diving reflex, but you still see it in warmer water too. It works when you hold your breath, you immerse your face in water or even just put something cold on your face. The combination of those two things will trigger this reflex."
Which is why his lab has been studying the phenomenon for several years.
“We had an undergraduate researcher in the lab, Veronica Gutierrez, who was looking for a project," Campbell recalls. " had just started reading about the diving reflex and was fascinated, and so I asked her: Do you want to teach mice how to dive? And she said, ‘Yes!’ She jumped into it, built a swimming pool for them, learned how to train them. We’ve been studying them now for a few years, and it works surprisingly well. Every mouse, every time shows this reflex.”
What’s more, the test subjects seemed to change over time:
“We noticed that the mice were just becoming easier to handle. They seemed less afraid of us, less stressed, and we had to wonder: Is this decrease in their heart rate actually effecting their mood?”
There was actually one sign the animals enjoyed the sensation produced by the diving reflex.
“It’s hard to know if they like it. You can’t really ask them, but I’ve been surprised to see a few times the mice will climb out of the water after a dive and then turn around and jump back in.”
And using a maze of closed and open channels, the laboratory found further evidence that mice who’d taken the plunge were, in fact, more relaxed.
“Anxious mice will tend to stay in the closed arms. They’re going to avoid predation, avoid open areas, and what we noticed is when we activated this nerve and decreased heart rate, the mice spent significantly more time exploring the open arms.”
Campbell says the reflex is triggered by something called the vagus nerve – action central for many involuntary functions in our bodies.
“Vagal nerve stimulation has been looked at as a way of treating a variety of diseases and conditions. Epilepsy is one of them, depression, obesity, even anxiety and stress now.”
With a better understanding of the diving reflex and the vagus nerve, he thinks scientists might develop better treatments for stress, anxiety and other medical conditions.
