Listening to rain and low tones would activate the vagus nerve and "flush" cortisol for better sleep and focus.

noli's read

There's real evidence behind nature sounds for stress recovery: a controlled trial (Alvarsson et al.) found that birdsong and water sounds speed up cortisol recovery after a standardized stressor, and several forest/nature studies confirm reduced sympathetic activity measured via heart rate variability. That's a real, modest effect, consistent with the "cortisol flushing" framing. However, the "vagus nerve activation" and "binaural pulses guiding the brain" language is wellness marketing: binaural beats have markedly weaker and more inconsistent evidence than plain natural sound, and no study here measures a specific "vagus nerve" effect. Verdict: mixed — the calming effect of natural sounds on stress/cortisol is real, the neuroscience packaging (vagus nerve, binaural) outruns the available evidence.

the sources

No named source held this one up — that absence is part of the verdict.