Con­nect­ing dots in autism re­search

Pin­point­ing when autis­tic spec­trum disor­ders man­i­fest in chil­dren

The McGill Daily - - Sci+Tech - Fer­nanda Pérez Gay Juárez The Mcgill Daily

Autism is a con­di­tion that af­fects one in 68 Amer­i­can ac­cord­ing to the U.S. Cen­tre for Con­trol and Disease Pre­ven­tion. Symp­toms like atyp­i­cal so­cial and com­mu­ni­ca­tion de­vel­op­ment, nar­row in­ter­ests, and repet­i­tive be­hav­iours man­i­fest dur­ing the first few years of life. Autism is a life­long con­di­tion, although it some­times ap­pears to al­le­vi­ate with age as the autis­tic child learns strate­gies to adapt to the so­cial world.

The com­plex­ity of Autis­tic Spec­trum Disor­ders

Over the past decades, the fields of psy­chol­ogy, psy­chi­a­try and neu­ro­science have strug­gled to de­fine the term “autism.” Cur­rently, sci­en­tists use the term “Autism Spec­trum Disor­ders” (ASD): a clin­i­cal la­bel that groups to­gether a range of con­di­tions that fall within a “spec­trum,” or con­tin­uum of sever­ity. So far there are no ac­cu­rate clin­i­cal tests to di­ag­nose autism: no blood tests, no brain scans or any type of phys­i­cal test­ing. Clin­i­cians can only rely on the ob­ser­va­tions of cer­tain be­hav­iors to make the di­ag­no­sis. With the emer­gence of brain func­tional imag­ing tech­niques that can look at pat­terns of brain ac­tiv­ity in real time, re­searchers have associated the un­der­ly­ing char­ac­ter­is­tics of this con­di­tion to atyp­i­cal “brain dy­nam­ics;” that is, the way dif­fer­ent re­gions con­nect and co­or­di­nate their ac­tiv­i­ties within the brain. How­ever, th­ese new neu­roimag­ing tech­niques are not rou­tinely used in clin­i­cal set­tings, and the iden­ti­fi­ca­tion of th­ese dif­fer­ences in brain ac­tiv­ity is only be­gin­ning to be ex­plored.

To com­pli­cate the pic­ture even more, the ge­net­ics of autism are very un­clear as well. Even if there is a clear hered­i­tary com­po­nent in most cases of autis­tic chil­dren, the ge­netic ba­sis dis­cov­ered so far does not fol­low a clear pat­tern. When they looked for vari­a­tion in each of the 23 pairs of hu­man chromo- somes, dif­fer­ent teams of re­searchers have iden­ti­fied changes re­lated to autism in twenty of them. More­over, said ge­netic ab­nor­mal­i­ties do not re­sem­ble each other: some genes are deleted, oth­ers are du­pli­cated. Alan Evans, a re­searcher of the Mon­treal Neu­ro­log­i­cal In­sti­tute, said “there are genes which, if you have a du­pli­ca­tion of the gene, the brain gets big­ger. If you have a dele­tion of the gene, the brain gets smaller. [Both of th­ese con­di­tions are] called autism.” Given the het­ero­gene­ity of both ge­net­ics and neu­roanatomy of autism, some re­searchers have sug­gested that ASD should be thought of as “the autisms,” cor­re­spond­ing to more than one con­di­tion with dif­fer­ent ge­netic and neu­ro­log­i­cal un­der­pin­nings.

State of the art in autism re­search

So, how should re­search ap­proach such a com­plex con­di­tion? Which as­pects of it should a re­searcher ad­dress? Ge­net­ics, be­hav­iour, re­sponses to new treat­ments, an­i­mal mod­els, de­vel­op­ment of the dis­or­der; th­ese are all valid and im­por­tant as­pects that are dis­cussed in cur­rent autism re­search. Dif­fer­ent types of re­search lines are be­ing de­vel­oped in lab­o­ra­to­ries and clin­i­cal cen­ters world­wide to try to un­der­stand the many sides of the dis­or­der, and this has re­sulted in a boom in sci­ence jour­nal­ism.

Us­ing web por­tals like Neu­ro­science News, any­one can eas­ily ac­cess ar­ti­cles on autism pub­lished in the last six months, cov­er­ing molec­u­lar in­ves­ti­ga­tions, an­i­mal mod­els, ge­netic as­sess­ments, sta­tis­ti­cal as­so­ci­a­tions, and neu­roimag­ing stud­ies. The abun­dance of ar­ti­cles can be over­whelm­ing for those who are not ex­perts on autism, but is still use­ful in un­der­stand­ing the im­pli­ca­tions of the ASD.

If there’s one thing most re­searchers agree on, con­sid­er­ing the ev­i­dence of atyp­i­cal brain dy­nam­ics men­tioned above, it is that the “ab­nor­mal” be­hav­iors seen in peo­ple with Autism Spec­trum Disor­ders are re­lated to the way their brains process in­for­ma­tion. The com­pu­ta­tions done through this brain pro­cess­ing re­sult in com­plex hu­man be­hav­iour; they con­sist of a long se­ries of steps, and are or­ga­nized at many cog­ni­tive lev­els. So far, the ques­tion re­mains: where and when in this long se­ries of steps do autis­tic chil­dren’s brains start to func­tion dif­fer­ently? Do they have trou­ble with at­tend­ing to and or­ga­niz­ing what we re­ceive through our five senses? Or is their con­di­tion re­lated to more com­plex func­tions, such as com­bin­ing the in­for­ma­tion and an­a­lyz­ing it?

Autism, brain net­works, and in­for­ma­tion pro­cess­ing

One of the stud­ies that caught my at­ten­tion in re­cent weeks was done here at Mcgill Uni­ver­sity. John Lewis, Alan Evans, and their col­leagues stud­ied 260 chil­dren with ei­ther low or high risk for autism. They mea­sured their brain con­nec­tions us­ing a new tech­nique called weighted Mag­netic Res­o­nance Imag­ing at 6, 12, and 24 months of age, to in­ves­ti­gate the way their brains are wired and how brain con­nec­tions de­velop. They aimed to iden­tify which ar­eas be­gin to de­velop dif­fer­ently from those in neu­rotyp­i­cal chil­dren, and when that hap­pens.

Mea­sur­ing con­nec­tions be­tween neu­ronal ar­eas in our brain pro­vides data on the stages of in­for­ma­tion pro­cess­ing. Weighted mag­netic imag­ing help iden­tify brain net­works by mea­sur­ing and map­ping the brain’s con­nec­tions. Iden­ti­fy­ing dif­fer­ences in brain con­nec­tions dur­ing brain de­vel­op­ment be­tween low-risk and high­risk in­di­vid­u­als pro­vides us with in­sights into the way that autis­tic brains func­tion. Th­ese re­searchers mea­sured strength and length of neu­ronal con­nec­tions and cor­re­lated them to “net­work ef­fi­ciency,” mean­ing how well this net­work func­tions con­sid­er­ing the num­ber and di­ver­sity of its con­nec­tions. They showed solid re­sults which in­di­cated that the brains of chil­dren with high risk for autism be­gin to show dif­fer­ent con­nec­tion pat­terns when the in­fants are six months old. The dif­fer­ences in con­nec­tions were seen mainly in ar­eas in­volv­ing pro­cess­ing of vi­sion and touch, although a larger set of ar­eas in­volved in sound and lan­guage was also af­fected later on. The study also showed a pos­i­tive cor­re­la­tion be­tween “net­work in­ef­fi­ciency” and symp­tom sever­ity. Their re­sults give us in­sights on when th­ese chil­dren be­gin to process in­for­ma­tion dif­fer­ently. In their orig­i­nal pa­per, ti­tled “The Emer­gence of Net­work In­ef­fi­cien­cies in in­fants with Autism Spec­trum Dis­or­der,” the re­searchers con­cluded that the so­cial dif­fer­ences and atyp­i­cal be­hav­iour ob­served in chil­dren with ASD might be the con­se­quence of dif­fer­ences in low-level pro­cess­ing, which refers to the com­pu­ta­tions done by our brain cor­tex to process sen­sory in­for­ma­tion.

Brain con­nec­tiv­ity is a very promis­ing ap­proach to link ge­net­ics and en­vi­ron­men­tal in­flu­ence, be­cause some of our brain con­nec­tions are in­born, but are then mod­i­fied by ex­pe­ri­ence to pro­vide neu­ral ba­sis be­hav­ior. One of the mer­its of the work done by th­ese re­searchers at Mcgill is that they have iden­ti­fied how soon th­ese brain sig­na­tures ap­pear. Ad­dress­ing where, when, and how this con­di­tion arises gives valu­able clues to why clin­i­cal man­i­fes­ta­tions arise later on.

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