Researchers find the organization of the human brain to be nearly ideal

Have you ever won­dered why the human brain evolved the way it did?

A new study by North­eastern physi­cist Dmitri Kri­oukov and his col­leagues sug­gests an answer: to expe­dite the transfer of infor­ma­tion from one brain region to another, enabling us to operate at peak capacity.

The paper, pub­lished in the July 3 issue of Nature Com­mu­ni­ca­tions, reveals that the struc­ture of the human brain has an almost ideal net­work of connections—the links that permit infor­ma­tion to travel from, say, the audi­tory cortex (respon­sible for hearing) to the motor cortex (respon­sible for move­ment) so we can do every­thing from raise our hand in class in response to a ques­tion to rock out to the beat of The 1975.

The find­ings rep­re­sent more than a con­fir­ma­tion of our evo­lu­tionary progress. They could have impor­tant impli­ca­tions for pin­pointing the cause of neu­ro­log­ical dis­or­ders and even­tu­ally devel­oping ther­a­pies to treat them.

“An optimal net­work in the brain would have the smallest number of con­nec­tions pos­sible, to min­i­mize cost, and at the same time it would have max­imum navigability—that is, the most direct path­ways for routing sig­nals from any pos­sible source to any pos­sible des­ti­na­tion,” says Kri­oukov. It’s a bal­ance, he explains, raising and low­ering his hands to indi­cate a scale. The study presents a new strategy to find the con­nec­tions that achieve that bal­ance or, as he puts it, “the sweet spot.”

Kri­oukov, an asso­ciate pro­fessor in the Depart­ment of Physics, studies net­works, from those related to mas­sive Internet datasets to those defining our brains. In the new research, he and his co-​​authors used sophis­ti­cated sta­tis­tical analyses based on Nobel lau­reate John Nash’s con­tri­bu­tions to game theory to con­struct a map of an ide­al­ized brain network—one that opti­mized the transfer of infor­ma­tion. They then com­pared the ide­al­ized map of the brain to a map of the brain’s real net­work and asked the ques­tion “How close are the two?”

Remark­ably so. They were sur­prised to learn that 89 per­cent of the con­nec­tions in the ide­al­ized brain net­work showed up in the real brain net­work as well. “That means the brain was evo­lu­tion­arily designed to be very, very close to what our algo­rithm shows,” says Krioukov.

The sci­en­tists’ strategy bucks tra­di­tion: It lets function—in this case, navigability—drive the struc­ture of the ide­al­ized net­work, thereby showing which links are essen­tial for optimal nav­i­ga­tion. Most researchers in the field, says Kri­oukov, build models of the real net­work first, and only then address func­tion, an approach that does not high­light the most cru­cial links.

The new strategy is also trans­fer­able to a variety of dis­ci­plines. The study, whose co-​​authors are at the Budapest Uni­ver­sity of Tech­nology and Eco­nomics, mapped six diverse nav­i­gable net­works in total, including that of the Internet, U.S. air­ports, and Hun­garian roads. The Hun­garian road net­work, for example, gave trav­elers the “luxury to go on a road trip without a map,” the authors wrote.

Future appli­ca­tions of the research cross dis­ci­plines, too. Knowing what links in a net­work are the most crit­ical for nav­i­ga­tion tells you where to focus pro­tec­tive mea­sures, whether the site is the Internet, road­ways, train routes, or flight pat­terns. “Con­versely, if you’re a good guy facing a ter­rorist net­work, you know what links to attack first,” says Kri­oukov. A sys­tems designer could locate the missing con­nec­tions nec­es­sary to max­i­mize the nav­i­ga­bility of a com­puter net­work and add them.

In the brain, the links existing in the ide­al­ized net­work are likely those required for normal brain func­tion, says Kri­oukov. He points to a maze of magenta and turquoise tan­gles coursing through a brain illus­tra­tion in his paper and traces the magenta trail, which is present in both the ideal and real brains. “So we sus­pect that they are the pri­mary can­di­dates to look at if some dis­ease develops—to see if they are dam­aged or broken.” Looking to the future, he spec­u­lates that once such links are iden­ti­fied, new drugs or sur­gical tech­niques could per­haps be devel­oped to target them and repair, or cir­cum­vent, the damage.

“At the end of the day, what we are trying to do is to fix the dis­eased net­work so that it can resume its normal func­tion,” says Krioukov.