The human brain remains the biggest mystery in biological science with research now having success in diagramming brain wiring as a means to understand how it works.
If you understand the wiring, you can better understand the appliance.
With that in mind, an important research focus has been the brain’s “connectome” — what the National Institutes of Health describes as “a map of the neural pathways that underlie human brain function.”
Last week, a Carnegie Mellon University-based study that included a University of Pittsburgh researcher described the use of diffusion MRI technology to show that the structural connections of each person’s connectome are as unique as a fingerprint.
Scientists already suspected as much.
“We are our own unique neural snowflake, unique to the self, and we thought it was true but couldn’t prove it. But this confirms it,” said Timothy Verstynen, a psychology professor in CMU’s Center for the Neural Basis of Cognition. “The biological wires of the brain are unique to you.”
But researchers were surprised to also discover that brain changes occur more quickly than previously thought and that the brain architecture of identical and fraternal twins and siblings are largely dissimilar.
The study, published last Tuesday in PLOS Computational Biology, found that the brain’s connectome on average changes 13 percent every 100 days. Those changes occur mostly from experiences rather than genetic factors and can include diet, environmental exposures, disease, mental endeavors and activities, among others.
“I think the speed at which we saw changes in the connectome over time surprised me,” Mr. Verstynen said. “We expected a slower rate of change, and I knew as a psychologist that the brain can change. But I didn’t realize in this case how quick that could be.”
The study was funded by and included researchers from the Army Research Laboratory, but it also included researchers from CMU, Pitt, the University of California, Santa Barbara and National Taiwan University. Knowing how the brain is wired can improve understanding of brain function and dysfunction, including the potential for new insights about Alzheimer’s disease, it says.
Wiring of the connectome involves key components of brain architecture including brain cells (neurons) interconnected by their cellular extensions (axons) and synapses between each pair of neurons, which make up the gray matter of the brain, all of which is insulated by white brain matter (myelin sheaths), similar to protective insulation on electrical wires.
These brain wires or pathways occur in different sized bundles known as fascicles — superhighways of the brain — all insulated by white matter and representing the architecture that served as the study focus.
Greater levels of myelin insulation allow chemical and electrical impulses to travel faster along brain wiring, enhancing function. Pianists, for example, develop thicker white matter in areas of the brain linking finger movement control to music-processing areas of the brain, allowing neural impulses to travel fast enough for fingers to play “Flight of the Bumblebee.”
During the study, researchers used imaging of 699 brains to determine point-by-point connections along the white-matter pathways of each brain.
Calculations were made, based on water diffusion along white-matter fibers, which is similar to studying water flow and pressure inside a garden hose, said Mr. Verstynen, who holds a Ph.D. in psychology.
Seventeen thousand tests of people’s local connectome led to nearly a 100 percent match, showing it can serve as a unique marker of human identity.
This new understanding eventually could lead to studies of whether people who think alike or have common experiences or diseases also have similar brain wiring. As such, study results “open a new door for probing the influence of pathological, genetic, social or environmental factors on the unique configuration of the human connectome,” the study concludes.
In another finding, the study determined a mere 12.5 percent similarity in brain architecture between identical twins and only a 5 percent similarity between fraternal twins, which was only a marginally stronger rate than siblings in general.
That reveals the larger impact of environmental rather than genetic factors in alterations of brain architecture, opening the way for determining whether “shared experiences including poverty or pathological disease” may be “reflected in our brain connections,” Mr. Verstynen said.
Bruce Fischl, a professor of radiology at Harvard Medical School who was not involved in the research, said the study offers some interesting contributions to brain science but largely confirms other studies that have used other methods to show that each person’s brain architecture is unique.
While the large bundles of brain wiring can be seen and studied, technical limitations make it difficult to study smaller bundles or local circuits within the gray matter, making connectivity a big unknown in human brain research.
The balance of local and long-range connectivity also is different in regions of the brain.
“We know very little about connectivity,” said the Harvard professor, who holds a Ph.D. in cognitive and neural systems.
“Certainly, the biggest mystery is consciousness and how it arises,” he said. “Network analysis has been popular over the past five to 10 years — using techniques developed in other fields such as computer and social network analysis to try to understand how brain networks are connected.”
David Templeton: dtempleton@post-gazette.com or 412-263-1578.
First Published: November 22, 2016, 5:00 a.m.
