\u0130ster insan, ister balina ya da fil olsun, bir\u00e7ok memelinin beyni detayl\u0131 k\u0131vr\u0131mlarla kapl\u0131d\u0131r. Yeni yap\u0131lan ara\u015ft\u0131rmaya g\u00f6re, bu k\u0131vr\u0131ml\u0131l\u0131\u011f\u0131n derecesi, \u00f6l\u00e7ekleme kanunu ad\u0131 verilen, ayn\u0131 zamanda k\u00e2\u011f\u0131d\u0131n k\u0131r\u0131\u015fmas\u0131n\u0131 da a\u00e7\u0131klayan bir matematiksel ili\u015fkiye g\u00f6re belirlenebiliyor. G\u00f6zlemlere g\u00f6re, memeli beyinlerinde g\u00f6r\u00fclen bu say\u0131s\u0131z farkl\u0131 yap\u0131, t\u00fcrden t\u00fcre de\u011fi\u015fiklik g\u00f6steren \u00e7\u00f6z\u00fclmesi g\u00fc\u00e7 geli\u015fim s\u00fcre\u00e7lerinden ziyade, ayn\u0131 basit fiziksel s\u00fcre\u00e7ten kaynaklan\u0131yor.<\/p>\n
Kaliforniya \u00dcniversitesi\u2019nden sinirbilimci Georg Striedter, biyolojide eldeki t\u00fcm verilere tam olarak uyan bir matematiksel ili\u015fkinin bulunmas\u0131n\u0131n \u00e7ok nadir oldu\u011funu s\u00f6yl\u00fcyor. Striedter, bir \u015feyler yakalanm\u0131\u015f olabilece\u011fini belirtiyor. \u00d6l\u00e7ekleme kanununun, tam geli\u015fmi\u015f beyinlerdeki k\u0131vr\u0131mlar\u0131n desenlerini a\u00e7\u0131klayabildi\u011fini, ancak geli\u015fmekte olan beyinlerde k\u0131vr\u0131mlar\u0131n nas\u0131l ortaya \u00e7\u0131kt\u0131\u011f\u0131n\u0131 a\u00e7\u0131klayamad\u0131\u011f\u0131n\u0131 da ekliyor.<\/p>\n
Memeli beyinlerindeki k\u0131vr\u0131mlar, korteksin yani n\u00f6ronlar\u0131n bulundu\u011fu gri maddenin d\u0131\u015f katman\u0131n\u0131n toplam alan\u0131n\u0131n artmas\u0131na sebep olmaktad\u0131r. K\u0131vr\u0131ml\u0131 korteksler t\u00fcm memelilerde bulunmaz. \u00d6rne\u011fin, fareler ve s\u0131\u00e7anlar d\u00fcz y\u00fczeyli, lizansefalik (lissencephalic) beyne sahiptir. Buna kar\u015f\u0131n primatlar, balinalar, k\u00f6pekler ve kediler k\u0131vr\u0131ml\u0131, jiransefalik (gyrencephalic) beyne sahiptir.<\/p>\n
On y\u0131llard\u0131r biliminsanlar\u0131 bir t\u00fcrdeki beynin k\u0131vr\u0131mlar\u0131n\u0131n miktar\u0131yla di\u011fer karakteristik \u00f6zellikler aras\u0131nda bir ili\u015fki olup olmad\u0131\u011f\u0131n\u0131 bulmakla u\u011fra\u015f\u0131yor. \u00d6rne\u011fin, beyni k\u00fc\u00e7\u00fck hayvanlar d\u00fcz bir beyne sahip olma e\u011filimi g\u00f6sterse de, korteksin toplam alan\u0131n\u0131n beynin d\u0131\u015f y\u00fczeyine olan oran\u0131yla \u00f6l\u00e7\u00fclen k\u0131vr\u0131mla\u015fma miktar\u0131yla beynin k\u00fctlesi aras\u0131nda net bir ili\u015fki bulunmuyor. \u00c7e\u015fitli hayvan t\u00fcrleri i\u00e7in k\u0131vr\u0131mla\u015fma-beyin k\u00fctlesi grafi\u011fi \u00e7\u0131kard\u0131\u011f\u0131m\u0131zda, verilerin t\u00fcm alana yay\u0131ld\u0131\u011f\u0131n\u0131 ve bir e\u011fri olu\u015fturamad\u0131klar\u0131n\u0131 g\u00f6r\u00fcyoruz. Benzer \u015fekilde, k\u0131vr\u0131mla\u015fma miktar\u0131 ile n\u00f6ron say\u0131s\u0131, korteksin toplam alan\u0131 ya da korteks kal\u0131nl\u0131\u011f\u0131 aras\u0131nda da net bir ili\u015fki bulunmuyor.<\/p>\n
Ama art\u0131k, Brezilya\u2019daki Rio de Janerio Federal \u00dcniversitesi\u2019nden sinirbilimci Suzana Herculano-Houzel ve fizik\u00e7i Bruno Mota, memelilerin beynindeki k\u0131vr\u0131mla\u015fmay\u0131 a\u00e7\u0131klayabilecek evrensel nitelikte matematiksel bir ili\u015fki bulduklar\u0131n\u0131 savl\u0131yor. \u0130kili, 62 farkl\u0131 t\u00fcrden ald\u0131klar\u0131 verileri kullanarak, korteks alan\u0131 ile korteks kal\u0131nl\u0131\u011f\u0131n\u0131n kare k\u00f6k\u00fcn\u00fcn \u00e7arp\u0131m\u0131 ile beynin d\u0131\u015f y\u00fczey alan\u0131 aras\u0131ndaki ili\u015fkinin grafi\u011fini \u00e7izdi. Ara\u015ft\u0131rmac\u0131lar\u0131n Science dergisinde belirtti\u011fine g\u00f6re, t\u00fcm veri noktalar\u0131, gerek jiransefalik gerek lizansefalik canl\u0131larda tek bir evrensel e\u011fri \u00fczerine oturuyor. Bu e\u011fri, toplam korteks alan\u0131yla kal\u0131nl\u0131\u011f\u0131n bile\u015fiminin, d\u0131\u015f y\u00fczey alan\u0131n 5\/4\u2019\u00fcnc\u00fc kuvvetiyle orant\u0131l\u0131 olarak artt\u0131\u011f\u0131n\u0131 g\u00f6steriyor; t\u0131pk\u0131 \u00e7emberin alan\u0131n\u0131n yar\u0131\u00e7ap\u0131n karesiyle orant\u0131l\u0131 \u015fekilde artmas\u0131 gibi.
\nKula\u011fa karma\u015f\u0131k gelse de, bu evrensel ili\u015fki k\u0131r\u0131\u015ft\u0131r\u0131lm\u0131\u015f k\u00e2\u011f\u0131t tomarlar\u0131n\u0131n a\u00e7\u0131klamas\u0131yla ayn\u0131. Herculano-Houzel bunu farkl\u0131 boyut ve kal\u0131nl\u0131kta k\u00e2\u011f\u0131tlar\u0131 k\u0131r\u0131\u015ft\u0131r\u0131p y\u00fczey alanlar\u0131n\u0131 \u00f6l\u00e7erek g\u00f6steriyor. Bu ili\u015fki, b\u00fck\u00fclm\u00fc\u015f k\u00e2\u011f\u0131d\u0131n, enerjisini en aza indirgeyecek \u015fekle girmesinden kaynaklan\u0131yor. Yani muhtemelen, k\u0131vr\u0131mla\u015fmada korteks de basit\u00e7e mekanik enerjisini en aza indirecek \u015fekle b\u00fcr\u00fcn\u00fcyor.<\/p>\n
Fakat Striedter k\u0131r\u0131\u015ft\u0131r\u0131lm\u0131\u015f k\u00e2\u011f\u0131tla kurulan bu analojinin tamamen g\u00fcvenilir olmad\u0131\u011f\u0131n\u0131 ileri s\u00fcr\u00fcyor. K\u00e2\u011f\u0131d\u0131n eller taraf\u0131ndan uygulanan d\u0131\u015f kuvvetlere maruz kald\u0131\u011f\u0131n\u0131, oysa kortekse etkiyen kuvvetlerin b\u00fcy\u00fck ihtimalle i\u00e7erden geldi\u011fini belirtiyor. Makale \u00fczerine yine Science\u2019da yay\u0131mlanan bir yorumun e\u015fyazarlar\u0131ndan olan Striedter, biliminsanlar\u0131n\u0131n hen\u00fcz bu kuvvetlerin nas\u0131l olu\u015fup k\u0131vr\u0131mla\u015fmaya sebep oldu\u011funu belirleyemediklerini s\u00f6yl\u00fcyor. Konuyla ilgili baz\u0131 modellerin, k\u0131vr\u0131mla\u015fmay\u0131, korteksin d\u0131\u015f katman\u0131n\u0131n i\u00e7 katman\u0131na g\u00f6re daha h\u0131zl\u0131 b\u00fcy\u00fcmesiyle a\u00e7\u0131klad\u0131\u011f\u0131n\u0131 da belirtiyor. \u201c\u00d6l\u00e7ekleme sadece bir konu\u201d diyen Striedter, \u201cbunun mekanizmas\u0131 ise bamba\u015fka bir konu\u201d diye ekliyor.<\/p>\n
Ne var ki, Herculano-Houzel\u2019e g\u00f6re durum farkl\u0131. Herculano-Houzel, geli\u015fimin her a\u015famas\u0131nda b\u00fcy\u00fcyen korteksin kafatas\u0131ndan gelen d\u0131\u015f kuvvete maruz kald\u0131\u011f\u0131n\u0131 belirtiyor. S\u0131n\u0131rl\u0131 bir alanda b\u00fcy\u00fcyen korteksin mutlaka k\u0131r\u0131\u015fmas\u0131 gerekti\u011fini ve her a\u015famada \u00f6l\u00e7ekleme ili\u015fkisinin sa\u011fland\u0131\u011f\u0131n\u0131 savunuyor. Bunun b\u00fcy\u00fcyen domuzlar \u00fczerinde test edilebilece\u011fini ve \u015fimdiki ad\u0131m\u0131n\u0131n bunu yapmak oldu\u011funu s\u00f6yleyen Herculano-Houzel, e\u011fer \u00f6l\u00e7ekleme ili\u015fkisinin geli\u015fimin t\u00fcm evrelerinde ge\u00e7erli oldu\u011fu sonucuna var\u0131l\u0131rsa, k\u0131vr\u0131mla\u015fmay\u0131 a\u00e7\u0131klamak i\u00e7in ba\u015fka bir mekanizmaya gerek kalmayaca\u011f\u0131n\u0131 belirtiyor.<\/p>\n","protected":false},"excerpt":{"rendered":"
\u0130ster insan, ister balina ya da fil olsun, bir\u00e7ok memelinin beyni detayl\u0131 k\u0131vr\u0131mlarla kapl\u0131d\u0131r. Yeni yap\u0131lan ara\u015ft\u0131rmaya g\u00f6re, bu k\u0131vr\u0131ml\u0131l\u0131\u011f\u0131n derecesi, \u00f6l\u00e7ekleme kanunu ad\u0131 verilen, ayn\u0131 zamanda k\u00e2\u011f\u0131d\u0131n k\u0131r\u0131\u015fmas\u0131n\u0131 da a\u00e7\u0131klayan bir matematiksel ili\u015fkiye g\u00f6re belirlenebiliyor. G\u00f6zlemlere g\u00f6re, memeli beyinlerinde g\u00f6r\u00fclen bu say\u0131s\u0131z farkl\u0131 yap\u0131, t\u00fcrden t\u00fcre de\u011fi\u015fiklik g\u00f6steren \u00e7\u00f6z\u00fclmesi g\u00fc\u00e7 geli\u015fim s\u00fcre\u00e7lerinden ziyade, ayn\u0131 […]<\/p>\n","protected":false},"author":786,"featured_media":19362,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[175,19,25,35],"tags":[254,208,347],"class_list":["post-3111","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-138-sayi","category-bilim-gundemi","category-matematik","category-noroloji","tag-beyin","tag-matematik","tag-noroloji"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/3111","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/users\/786"}],"replies":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/comments?post=3111"}],"version-history":[{"count":0,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/3111\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media\/19362"}],"wp:attachment":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media?parent=3111"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/categories?post=3111"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/tags?post=3111"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}