Sunday, June 19, 2016

Youth, Age and Fractal Complexity


The Real Secret of Youth Is Complexity
Our physiological processes become increasingly simple as we age. 
Simplicity, simplicity, simplicity!” Henry David Thoreau exhorted in his 1854 memoir Walden, in which he extolled the virtues of a “Spartan-like” life. Saint Thomas Aquinas preached that simplicity brings one closer to God. Isaac Newton believed it leads to truth. The process of simplification, we’re told, can illuminate beauty, strip away needless clutter and stress, and help us focus on what really matters.

It can also be a sign of aging. Youthful health and vigor depend, in many ways, on complexity. Bones get strength from elaborate scaffolds of connective tissue. Mental acuity arises from interconnected webs of neurons. Even seemingly simple bodily functions like heartbeat rely on interacting networks of metabolic controls, signaling pathways, genetic switches, and circadian rhythms. As our bodies age, these anatomic structures and physiologic processes lose complexity, making them less resilient and ultimately leading to frailty and disease.

To understand this loss, we must first define what we mean by “complexity” in the scientific sense. Consider a Rube Goldberg machine, in which one action leads to another, then another, and so on in linear fashion to finally, say, scratch one’s back or bring a napkin to one’s mouth. Although this over-engineered contraption may look complicated, it’s actually quite simple: A given input always produces the same output. Its simplicity makes its behavior easy to predict. It also makes the system vulnerable because a single break in the chain will undermine its entire function.
A complex process, in contrast, involves multiple different components interacting across multiple scales in time and space. Because these interactions are nonlinear, outputs are not proportional to inputs and thus are more erratic and unpredictable. For instance, think of what it takes just to lift your foot. Electrical, chemical, and mechanical parts must continually coordinate across molecular, cellular, organ, and systemic levels. Genetic machinery inside cells generate proteins to power muscles; gastrointestinal organs digest and metabolize sugars to provide energy; motor centers in the brain plan and command movement, while nerves relay these messages to muscle fibers and deliver feedback to the brain about your foot’s location in space. As a whole, the process is something more than the sum of its parts.
The fractal-like networks of tissue in our brains, bones, kidneys, and skin all lose structural complexity as we age.
We can quantify the complexity of biological systems by borrowing mathematical ideas from chaos theory and the fields of nonlinear dynamics and statistical physics. One of these is the concept of fractals. A fractal is an irregular geometric object whose shape obeys an underlying pattern: It appears similar to itself on multiple measurement scales. Clouds, coastlines, trees, rivers, mountain ranges, and fault lines are all examples of fractal-like structures. Whether examined from an airplane or on the ground, with a magnifying glass or a microscope, their appearance stays generally the same.

Inside the body, arteries, neurons, bones, and bronchi are organized in a similar way. And if we measure across time rather than space, we also see fractal patterns in the moment-to-moment fluctuations in physiologic signals, including heart and breathing rates, blood pressure, brain waves, and hormonal secretions. Contrary to what you might expect, these fluctuations don’t follow regular, or periodic, patterns, but instead show a complex type of variability—what’s known as “deterministic chaos.” Although the oscillations are irregular, they appear self-similar when observed over seconds, minutes, hours, or days....MORE