Dr. Andrew Huberman is a neuroscientist and tenured professor in the Department of Neurobiology at Stanford University School of Medicine. He is an expert in neuroplasticity, and his work in the Huberman Lab has been featured in Science, Discover, Scientific American, Time, the New York Times, and countless peer-reviewed journals. He recently sat with Rich Roll and the double breath inhale / extended exhale technique to bust stress was discussed. It is a great technique for monkey brain that one hears little to nothing about.
Here it is. Physiological sigh.
Here's Huberman showing the technique on another podcast.