professors at Baylor College of Medicine in Houston have led us one
giant step closer to learning about how pigeons, and perhaps other birds
and animals, navigate their way home. We know that they rely on the
Earth's magnetic field, but we know less about their brain's neural
mechanisms that allow the magnetic reception. The Baylor scientists
found 53 neural cells that respond, dubbing them the pigeons GPS cells.
Previously, magnetic receptors have been identified by researchers in the retina, nose or beak, and inner ear of vertebrates, and expression markers have been identified in various brain regions activated by magnetic stimulation, but the Baylor study actually sought to identify the central neural mechanisms, the single cell activity, that is responsible for coding magnetic field direction.
David Dickman and colleague Le-Qing Wu identified 53 individual cells that were stimulated by changes in the magnetic field and, in their experiments, they held pigeons still while the magnetic fields around the pigeons were altered, measuring each electrical signal with sensors.
Each of the 53 neurons responded differently to the magnetic field, but they all responded with a compass-like reading up or down, north/south directionally, and their positions in relation to those poles. Each of the GPS cells also varied in strength in response to the changes in the experimental magnetic fields, but the strongest responses were to the actual magnetic field of the earth.
"People had reported in the past... that birds do not seem to respond to the polarity of the magnetic field, yet here we have neurons that are in fact doing that," Prof Dickman told BBC News.
"That's one of the beautiful aspects of what we've identified, because it shows how single brain cells can record multiple properties or complex qualities in a simple way."