Simply looking at nature – or even just digital pictures of it – can relieve pain, according to new research which scanned the brains of people receiving electrical shocks.

Nature's many health benefits have been documented by decades of research.

More than 40 years ago, a pioneering study showed that hospitalized patients needed fewer painkillers and recovered quicker when they looked out of a window onto green space rather than a brick wall.

"Yet until now, the underlying reasons for this effect were unclear," said Maximilian Steininger, a neuroscientist at the University of Vienna and lead author of a study published in Nature Communications on Thursday.

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The problem is that both nature and pain can be subjective.

Because people like nature, it could have a placebo effect. Or what if it is not nature that reduces pain, but city life that increases it?

To find out more, the researchers recorded the brain activity of 49 volunteers using functional magnetic resonance imaging (fRMI.)

The subjects looked at different images while receiving a series of electric shocks – some more painful than others – on the back of their left hand.

The first scene depicted a lake surrounded by trees blowing in the wind, while the sounds of rustling leaves and birdsong played in the background.

In the second scene, some urban elements such as buildings, benches, and alleyways were added, while city noise intruded.

The third scene was of an office, with the accompanying drab furniture and whir of work.

Not only did the participants report feeling less pain when they looked at the natural landscapes, the fMRI scans showed there was a difference in their brains.

"Our study is the first to provide evidence from brain scans that this isn't just a placebo effect," Steininger said in a statement.

The nature scenes provoked decreased activity in a part of the brain involved in perceiving pain, called nociception. However, other areas linked to regulating pain were not significantly affected.

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The researchers said the results could be because natural environments capture people's attention, diverting them away from the sensation of pain.

This is known in psychology as the "attention restoration theory."

"The fact that this pain-relieving effect can be achieved through a virtual nature exposure which is easy to administer has important practical implications," said study co-author Alex Smalley from the UK's Exeter University.

It also "opens new avenues for research to better understand how nature impacts our minds," he added.