You've just turned up at a research lab and you're told that, in a few minutes' time, you will have to give a speech to an unknown audience. You're not told what you will be asked to speak about until you get to the room where there is a microphone and four people sitting behind a desk at the far end. You are then asked to talk about you personal qualifications as if you were applying for a job, explaining why you are a better candidate for the job than any other applicants. And you have to keep going for five minutes.
As soon as the public speaking task is finished, you're given a mental arithmetic task, still in front of the audience. You are instructed to calculate backwards in steps of 17 from the number 2043:
'2043, 2026, 2009, 1992...'
However, every time you make a mistake, you're told to start again, from 2043.
By this point, you may well be wondering why you signed up to take part in this research. You're probably feeling pretty stressed. Of course, that's the point. This procedure is called the Trier Social Stress Test (TSST) and it's designed to activate both of your biological stress response systems. That's the immediate fight-or-flight system, and the longer-term chronic stress system, called the HPA axis. What this means is that after the public speaking and mental arithmetic tasks you'll be releasing significantly higher levels of ACTH, and cortisol, and increased heart rate.
The effect of rippling water
But what if relaxing sounds could help to modify the way your body responds to this stress? That's what a recent study set out to examine. 60 female participants were split into three groups. Before they went through the TSST: twenty of them had a ten minute rest period, twenty listed to the sound of rippling water, and twenty listened to music. All the music people were given the same piece - Miserere. That's a 17th century choral piece by an Italian composer called Allegri. This was chosen because previous research has found it to be relaxing and pleasant. Also, giving people music that has been identified scientifically as being relaxing is more effective than allowing people to choose their own relaxing music.
The group who listened to the music had the highest cortisol levels of all three groups when tested regularly up to an hour after the TSST. This wasn't means that listening to what the researchers were expecting - that the people who listened to calm, relaxing music should end up more stressed than people who simply sat and rested. Their suggested explanation was that listening to music activates some of the neural networks also used by the HPA axis. In other words, the HPA axis had been given a slight head-start by the music which was then boosted further by the TSST.
By contrast, the people who listened to rippling water had the lowest cortisol levels of all three groups. This points to the idea that our evolutionary past is still wired into our stress response systems. Our brains have developed, through pretty much the entirety of human evolution, to the sounds of nature. Becoming detached from that is therefore to put us into what the brain unconsciously senses as an unnatural state. Or, to put it the other way around, the brain is comforted by the sounds of nature because this feels more normal. And when things are normal, there is no need to be on alert, no need to trigger the stress responses such as the HPA axis.