Over the past year, reports have flown right and left touting the positive mental health effects of looking at nature — even a photograph will make you feel better, the studies said.But humans, it seems, are just as predisposed to relax from listening to nature sounds, even without a visual: virtual reality forests that include nature sounds soothe stressed participants more effectively than when the sound is muted; birdsong has been linked to lower biological measures of stress. And anecdotes of ocean waves and rainfall alleviating anxiety abound. What is it about such different sounds – ocean waves, birdsong, wind rustling leaves, all loosely similar under the badge of ‘nature’ – that uplifts us?

Human hearing is one of the earliest information processing senses to develop; foetuses can hear as early as 18 weeks in utero. It’s “an alarming sensory system, which alarms us about the dangers,” says Rajalakshmi K., Ph.D., an audiologist with the All India Institute of Speech and Hearing (AIISH) who focuses on psychoacoustics, that is, the way sound is perceived.

One of the first sounds early humans would hear would have originated in nature. Any effect birdsong or the sound of leaves rustling, or brooks babbling – or even human vocalizations — have on our minds “is evolutionary,” she says. These sounds take us back to our earliest roots and tap into a kind of primordial connection between living things; studies have shown time spent in nature increases feelings of connectedness to others and to the wider world.

By way of evidence, too, Rajalakshmi points to increased rates of depression among people who have lost their hearing. “It withdraws you,” she says, “the forced silence.”

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But our long familiarity with nature sounds might be rivaled by the, well, nature of the sounds, when it comes to boosting mental wellbeing. A 1989 theory by Rachel and Stephen Kaplan, professors of psychology at the University of Michigan, suggests nature has a quality of “soft fascination” that when looked at captures attention effortlessly, requiring less or no effort from the brain to engage — thus easing a fatigued mind. This came to be known as Attention Restoration Theory (ART), which gradually expanded, through their research and others’, to include exposure to nature via hearing and other senses.

ART has been criticized for its vagueness in defining soft fascination, which leaves it wide open to interpretation. One way to think of it, as it relates to hearing, could be around the balance of noises that make up the sound. Manmade sounds that often lead to aggravation have an unnatural pattern to them – think of the random cacophony of honking car horns, or the perfect repetition of a jackhammer. Natural sounds, by contrast, have a pattern without having uniformity – a “rhythm,” says Dr. Rahul Ratan Bagale, a psychiatrist with Apollo Clinic in Pune.

“Waves come and go, and they come again,” he adds. “[The rhythm] becomes a tool for our minds to focus” – one that “distracts from the mind-chatter.”

This helps us achieve a mindful state, one in which “we know what thoughts we consume, and what sensations have an impact on our mental health, and in what proportion,” he explains, thus improving our mental wellbeing.

It’s a meditative exercise that may manipulate actual brain function in a way that eases stress.

“When we listen to any kind of harmonious vibration, rhythmic vibration [such as nature sounds], it actually has a very deep impact on our brain,” says Maestro Satya Brat, a sound therapist and head of the Academy of Sound Healing in Kolkata.

From the aum at the birth of the universe (arguably the original sound of nature), to the Ancient Greek physicians’ use of vibration to treat mental disturbance, humans sussed out long ago that certain sounds affect the frequency at which our brains operate – and that the frequency, or waves, of our brains are related to our conscious mental states. Modern scientific evidence of this is nascent at best, but one point experts do agree on is a relationship of some kind between brain waves and mental illness.

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“… gamma rhythms are clearly disturbed in a number of psychiatric conditions,” Dr. Vikaas Sohal, Ph.D., M.D., a systems neuroscientist at the University of California, San Francisco, told Scientific American in 2018.

Our brains operate across five different frequencies — gamma, beta, alpha, theta, and delta — with brain waves measurable on the spectrum as hertz. At gamma frequency, or rhythms, our brain waves are fastest; we are at peak concentration and focus, using many different parts of our brain simultaneously to process information. At beta, our waves are a little less quick, our minds very active, engaged, and alert; this is the primary state of our waking hours. Alpha waves are the warm down from beta state; our brains are on a break, taking a mindful pause. If alpha state is a pause in our thoughts and focus, then theta waves are an actual departure from them – a relaxed mind wandering, daydreaming, zoning out, or falling asleep. And delta waves are the slowest frequency, producing a deep unconscious state, as in a dreamless sleep.

Both alpha and theta waves have been linked to the kind of mindful, meditative state that can come from listening to nature. They also broadly reflect the functioning of the brain’s Default Mode Network (DMN), a system of interaction between brain regions that kicks in whenever we’re not focused on an external task – our background hum, or internal stream of consciousness, so to speak. Research has shown the DMN functions differently depending on what sounds we hear. A 2017 study using MRI scans revealed when we listen to nature sounds, DMN activity reflects thinking and focus directed externally to our selves. When listening to artificial sounds, DMN connectivity reflects attention directed inward, “similar to states observed in anxiety, post-traumatic stress disorder and depression.” In the study, the most-stressed participants benefited most from listening to the nature recordings.

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Nature is, arguably, the antithesis of silence. Most people in search of ‘peace and quiet’ gravitate to rural or untouched environments where sound is natural and plentiful, but not overwhelming or chaotic. Full silence in nature is often a warning itself, reflecting the presence of a predator, or an impending natural disaster. Perhaps it is for this reason that a person sitting in the quietest place on Earth – a manmade anechoic chamber in the U.S. that registers negative decibels – will start to hallucinate. The longest anyone has lasted in the chamber is only 45 minutes.

The last year will go on record as the quietest year in recorded human history, as pandemic lockdowns around the world shut down human activity and industry for months. Incidentally, the year also witnessed the most mass trauma in 80 years and a global mental health crisis prompted by a very natural cause – a virus communicated from an animal to a human. Nature sounds may demonstrably boost our feelings of wellbeing, but they are not miracle cures for the wider world. Or maybe they are – we just have to listen more closely.

“Finally, the Earth could hear itself think, and the voice of its thought was birdsong,” writes Steven Lovatt, whose book, Birdsong in a Time of Silence, chronicles the resurgence of nature sounds during the early months of the Covid19 pandemic. “A year on, we’re still too close to it to tell which stories and emotions will survive from that strangest of times. But it also seemed possible, even in the grimmest days, that the spring of 2020 might be remembered differently – as the time when we first heard the birds and, hearing them, began to recover an appreciation of something universal we had somehow mislaid.”