Neuronal tracing reveals that Cluster N receives input through the thalamofugal visual pathway. Schematic side view of the bird’s brain indicating the locations of tracer application. Retrograde tracer (BDA, shown in green) was iontophoretically applied into Cluster N (shown in magenta). Anterograde tracer (CtB, shown in red) was injected into the vitreous of the contralateral eye. (Credit: Image courtesy of PLoS and article authors, Heyers D, Manns M, Luksch H, Gunturkun O, Mouritsen H)
For years, naturalists have been aware that migrating birds navigate according to the Earth’s magnetic field, as opposed to other cues. An “internal compass” is one way this phenomenon has been described. Now researchers have uncovered the mechanism behind this internal compass – in the eyes.
Cryptochromes, which fulfill the molecular requirements for sensing the magnetic reference direction, have recently been found in retinal neurons of migratory birds (Mouritsen et al., PNAS, 2004).
Furthermore, studies investigating what parts of a migratory bird´s brain are active when the birds use their magnetic compass showed that the cryptochrome-containing neurons in the eye and a forebrain region (“Cluster N”; Mouritsen et al., PNAS, 2005; Liedvogel et al., EJN, 2007) are highly active during processing of magnetic compass information in migratory birds.
That’s a nifty trait to evolve.
- Do Migratory Birds ‘See’ The Magnetic Field? – ScienceDaily
- Birds Can “See” Earth’s Magnetic Field – National Geographic
- Heyers D, Manns M, Luksch H, Gunturkun O, Mouritsen H. A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds.
PLoS One 2007 Sep 26;2(9):e937.
- Mouritsen H, Janssen-Bienhold U, Liedvogel M, Feenders G, Stalleicken J, Dirks P, Weiler R. Cryptochromes and neuronal-activity markers colocalize in the retina of migratory birds during magnetic orientation.
Proc Natl Acad Sci U S A. 2004 Sep 28;101(39):14294-9.
- Liedvogel M, Feenders G, Wada K, Troje NF, Jarvis ED, Mouritsen H. Lateralized activation of Cluster N in the brains of migratory songbirds.
Eur J Neurosci. 2007 Feb;25(4):1166-73.
- Bird Migration – Wikipedia