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August 03, 2010

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Brain lives at “edge of chaos”

March 18, 2009
Courtesy Public Library of Science
and World Science staff

U.K. re­search­ers are of­fer­ing new ev­i­dence that the hu­man brain lives “on the edge of chaos,” at a crit­i­cal tran­si­tion point be­tween ran­dom­ness and or­der. 

The stu­dy, pub­lished March 20 in the re­search jour­nal PLoS Com­puta­t­ional Bi­ol­o­gy, pro­vides ex­pe­ri­men­tal da­ta on an idea pre­vi­ously fraught with the­o­ret­i­cal specula­t­ion.

Sci­en­tists have iden­ti­fied a phe­nom­e­non they call self-or­gan­ized crit­i­cal­ity—where sys­tems spon­ta­ne­ously or­gan­ize them­selves to op­er­ate at the bor­derline be­tween or­der and chaos—in many dif­fer­ent phys­i­cal sys­tems, in­clud­ing avalanches, for­est fires, earth­quakes, and heart rhythms. 

Ac­cord­ing to the stu­dy, by a team from the Uni­ver­s­ity of Cam­bridge, the Med­i­cal Re­search Coun­cil Cog­ni­tion & Brain Sci­ences Un­it, and the Glax­o­SmithK­line Clin­i­cal Un­it Cam­bridge, hu­man brain net­work dy­nam­ics have some­thing im­por­tant in com­mon with some su­per­fi­cially very dif­fer­ent sys­tems in na­ture.

Com­puta­t­ional net­works show­ing these char­ac­ter­is­tics have al­so been shown to have the best mem­o­ry and in­forma­t­ion-processing ca­pacity, re­search­ers say: crit­i­cal sys­tems can re­spond quickly and ex­ten­sively to small changes in their in­puts.

“Due to these char­ac­ter­is­tics, self-or­gan­ized crit­i­cal­ity is in­tu­i­tively at­trac­tive as a mod­el for brain func­tions such as per­cep­tion and ac­tion, be­cause it would al­low us to switch quickly be­tween men­tal states in or­der to re­spond to chang­ing en­vi­ron­men­tal con­di­tions,” said co-author Man­fred Kitzbich­ler of Cam­bridge.

The re­search­ers used brain im­ag­ing tech­niques to meas­ure dy­nam­ic changes in the syn­chron­iz­a­tion of ac­ti­vity be­tween dif­fer­ent re­gions of the func­tion­al net­work in the hu­man brain. They al­so in­ves­t­i­gated the syn­chron­iz­a­tion of ac­ti­vity in com­puta­t­ional mod­els, and found that the “dy­nam­ic pro­file” they had iden­ti­fied in the brain was ex­actly re­flected in the mod­els. 

“A nat­u­ral next ques­tion we plan to ad­dress in fu­ture re­search will be: How do meas­ures of crit­i­cal dy­nam­ics re­late to cog­ni­tive per­for­mance or neu­ro­psy­chi­atric disor­ders and their treat­ments?” said Kitzbich­ler.

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Researchers at Cambridge Un ivers ity are offering new evidence that the human brain lives “on the edge of chaos,” at a critical transition point between randomness and order. The study, published March 20 in the research journal PLoS Comput ational Biology, provides experi mental data on an idea previous ly fraught with theoretical specul ation. Scientists have identified a phenomenon they call self-organized critical ity—where systems spontaneous ly organize themselves to operate at the borderline between order and chaos—in many different physical systems, including avalanches, forest fires, earthquakes, and heart rhythms. According to the study, by a team from the Un ivers ity of Cambridge, the Medical Research Council Cognition & Brain Sciences Un it, and the GlaxoSmithKline Clinical Un it Cambridge, human brain network dynamics have something important in common with some superficial ly very different systems in nature. Comput ational networks showing these character istics have also been shown to have the best memory and inform ation-processing capac ity, researchers say. In particular, critical systems are able to respond very rapid ly and extensive ly to minor changes in their inputs. “Due to these character istics, self-organized critical ity is intuitive ly attractive as a model for brain functions such as perception and action, because it would allow us to switch quick ly between mental states in order to respond to changing environmental conditions,” said co-author Manfred Kitzbichler of Cambridge. The researchers used brain imaging techniques to measure dynamic changes in the synchron ization of activ ity between different regions of the functional network in the human brain. They also investigated the synchron ization of activ ity in comput ational models, and found that the “dynamic profile” they had identified in the brain was exact ly reflected in the models. “A natural next question we plan to address in future research will be: How do measures of critical dynamics relate to cognitive performance or neuropsychiatric disorders and their treatments?” said Kitzbichler.