Mechanical coherence offers a template for understanding "personal coherence."

Heart rate variability measures offer a good measure of personal coherence.

Social coherence proposes to measure the physiological synchrony among groups of people.

HRV biofeedback is one proposed measure of social coherence.

If you have ever marveled at a murmuration of starlings or the harmonious motions of a school of fish, you may have wondered how these species achieve such communion of action. Apparently, even the biologists who study such questions are still wondering. By what instinct can thousands of birds fly as a coherent unit? They don’t need to practice for hours, days, and weeks on end, like our marching bands. And yet, we humans might also have some instinct for harmony.

In the practice of psychiatry, we like to think we have better radar than most doctors for identifying incoherent thinking in our fellow humans. Incoherence is one of the crucial signs for potential disasters in the central nervous system—delirium, psychosis, mania, intoxication, stroke, encephalitis. And yet, now in the waning years of my career, I confess that I’ve practiced this skill of identifying incoherent thinking with only the vaguest definition of coherence, and no measure. For me and most of my colleagues, identifying the incoherent mind is more of an art than a science.

But writing a book recently about our stress response system (Toxic Stress, 2024) got me thinking we doctors—no, all clinicians—should take a closer look at how we think about coherence on several levels, and take a tip from engineers. In the engineering world mechanical coherence refers to the extent to which two or more oscillating systems are synchronized, or coherent. The laser beam, for example, synchronizes two bands of light, both temporally and spatially, to achieve a sharp focus and a narrow frequency, a highly coherent light system compared to sunlight.

To the extent that we can think of our body as a complex system of systems, particularly our stress response system, does it make sense to ask if our bodies operate by some form of mechanical........

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