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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.

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.

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.