鳥兒怎樣找到回家的路,？所有人都同意動物能夠利用地球磁場來形成一個體內“羅盤”以感應方向的說法,，但人們觀點的一致性也就到此為止,。
一些研究人員提出這樣一個觀點：磁性是由鳥喙中連接到三叉神經上的磁體來探測的,；另一些研究人員則認為,，磁性是通過眼睛經由一個復雜的光敏機制來傳導的,。對后一個觀點（即有關眼睛所起作用的觀點）的支持,，來自對歐洲知更鳥的一項神經外科和行為學研究。在腦中一個被稱為“cluster N”的中心有病灶的鳥被發(fā)現缺乏磁定向能力,。而且至少在這種候鳥中,，其喙中假設存在的磁受體在磁性羅盤定向中沒有起作用。（生物谷Bioon.com）
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生物谷推薦原始出處：
Nature 461, 1274-1277 (29 October 2009) | doi:10.1038/nature08528
Visual but not trigeminal mediation of magnetic compass information in a migratory bird
Manuela Zapka1, Dominik Heyers1, Christine M. Hein1, Svenja Engels1, Nils-Lasse Schneider1, J?rg Hans1, Simon Weiler1, David Dreyer1, Dmitry Kishkinev1, J. Martin Wild2 & Henrik Mouritsen1
1 AG Neurosensorik/Animal Navigation, IBU, University of Oldenburg, D-26111 Oldenburg, Germany
2 Department of Anatomy, Faculty of Medical and Health Sciences, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
Correspondence to: Henrik Mouritsen1 Correspondence and requests for materials should be addressed to H.M.
Magnetic compass information has a key role in bird orientation1, 2, 3, but the physiological mechanisms enabling birds to sense the Earth's magnetic field remain one of the unresolved mysteries in biology2, 4. Two biophysical mechanisms have become established as the most promising magnetodetection candidates. The iron-mineral-based hypothesis suggests that magnetic information is detected by magnetoreceptors in the upper beak and transmitted through the ophthalmic branch of the trigeminal nerve to the brain5, 6, 7, 8, 9, 10. The light-dependent hypothesis suggests that magnetic field direction is sensed by radical pair-forming photopigments in the eyes11, 12, 13, 14, 15 and that this visual signal is processed in cluster N, a specialized, night-time active, light-processing forebrain region16, 17, 18, 19. Here we report that European robins with bilateral lesions of cluster N are unable to show oriented magnetic-compass-guided behaviour but are able to perform sun compass and star compass orientation behaviour. In contrast, bilateral section of the ophthalmic branch of the trigeminal nerve in European robins did not influence the birds' ability to use their magnetic compass for orientation. These data show that cluster N is required for magnetic compass orientation in this species and indicate that it may be specifically involved in processing of magnetic compass information. Furthermore, the data strongly suggest that a vision-mediated mechanism underlies the magnetic compass in this migratory songbird, and that the putative iron-mineral-based receptors in the upper beak connected to the brain by the trigeminal nerve6, 7, 8 are neither necessary nor sufficient for magnetic compass orientation in European robins.
