A walk in the woods—or even a sound machine that plays recordings from nature—can affect heart rate and alter connections in the brain, say researchers.  (Amanda MacMillan April 05, 2017)

You know that feeling of clear-headed calm that washes over you when you listen to water babbling down a stream, or leaves rustling in the wind? Researchers say they’ve pinpointed a scientific explanation for why sounds from nature have such a restorative effect on our psyche: According to a new study, they physically alter the connections in our brains, reducing our body’s Natural fight-or-flight instinct.

Natural sounds and green environments have been linked with relaxation and well-being for hundreds of years, of course. But the new research, published in the journal Scientific Reports, is the first to use brain scans, heart-rate monitors, and behavioral experiments to suggest a physiological cause for these effects.

To investigate the connection between the brain, the body, and background noise, researchers at Brighton and Sussex Medical School in England recruited 17 healthy adults to receive functional magnetic resonance imaging (fMRI) scans while listening to a series of five-minute soundscapes of natural and manmade environments.

During each soundscape, participants also performed a task to measure their attention and reaction time. Their heart rates were monitored as well, to indicate changes in their autonomic nervous systems—the system of organs involved in involuntary processes such as breathing, blood pressure, temperature, metabolism, and digestion.

When they studied the fMRI results, the researchers noticed that activity in the brain’s default mode network—an area involved in mind wandering and “task-free” states of wakefulness—varied depending on the background sounds being played. Specifically, listening to artificial sounds was associated with patterns of inward-focused attention, while Nature Sounds prompted more external-focused attention.

Inward-focused attention can include worrying and rumination about things specific to one's self—patterns that have been linked to conditions involving psychological stress (including depression, anxiety, and post-traumatic stress disorder). Participants’ reaction times were slower when they listened to artificial sounds compared to natural ones, as well.

Slight differences in heart rate were also detected, indicating a shift in the body’s autonomic nervous system response.  Overall, nature sounds were associated with a decrease in the body’s sympathetic response (which causes that “fight-or-flight” feeling) and an increase in parasympathetic response—the one that helps the body relax and function in normal circumstances, and is sometimes referred to as the “rest-digest” response.

Those results weren’t the same for everyone, though: People who started the study with the highest sympathetic responses (suggesting high levels of stress) registered the biggest relaxation benefits from the nature clips. People who started with low levels of sympathetic response, on the other hand, actually had a slight increase when listening to natural versus artificial sounds.

(courtesy of health.com)