Despite the brain’s complexity, a growth pattrn places complementary neurons in proximity to each other:
“How do cells with complementary functions arrange themselves to construct a functioning tissue?” said study co-author Bo Wang, an assistant professor of Bioengineering. “We chose to answer that question by studying a brain because it had been commonly assumed that the brain was too complex to have a simple patterning rule. We surprised ourselves when we discovered there was, in fact, such a rule.”
The brain they chose to examine belonged to a planarian, a millimeter-long flatworm that can regrow a new head every time after amputation. First, Wang and Margarita Khariton, a graduate student in his lab, used fluorescent stains to mark different types of neurons in the flatworm. They then used high-resolution microscopes to capture images of the whole brain — glowing neurons and all — and analyzed the patterns to see if they could extract from them the mathematical rules guiding their construction.
What they found was that each neuron is surrounded by roughly a dozen neighbors similar to itself, but that interspersed among them are other kinds of neurons. This unique arrangement means that no single neuron sits flush against its twin, while still allowing different types of complementary neurons to be close enough to work together to complete tasks.
The researchers found that this pattern repeats over and over across the entire flatworm brain to form a continuous neural network. Study co-authors Jian Qin, an assistant professor of chemical engineering, and postdoctoral scholar Xian Kong developed a computational model to show that this complex network of functional neighborhoods stems from the tendency of neurons to pack together as closely as possible without being too close to other neurons of the same type.
While neuroscientists might someday adapt this methodology to study neuronal patterning in the human brain, the Stanford researchers believe the technique could be more usefully applied to the emerging field of tissue engineering.Tom Abate, Stanford School of Engineering, “Scientists discover the mathematical rules underpinning brain growth” at ScienceDaily
It’s reminiscent of the finding that a rat’s whiskers don’t emerge randomly but rather from a Euler spiral. In a designed universe, we should expect this. It is not natural selection acting aimlessly on random mutation but rather the designs implicit in the universe enacted as the organism comes into existence—because they are the simplest ones under the circumstances.
See also: The design of life, even in a rat’s whiskers: There is no reason to believe that the rat went through hundreds of flopped, fatal designs for whiskers (natural selection acting on random mutation) before hitting on the Euler spiral. It was probably implicit from the beginning because the nature of reality in our universe would enact it. As a line of least resistance.