Many birds have a sixth sense. No, not
seeing dead people: they detect the Earth's magnetic field.
This ability allows them to return to the
same places year after year during seasonal migration.
Now scientists are closer to identifying
the mechanism our feathered friends use to detect the Earth's magnetic field, involving
quantum mechanics in their eyes.
Cryptochrome-4: a bird's magnetic sensor
The research team is led by scientists from
the University of Oldenburg in Germany and the University of Oxford.
It has been studying a protein known as cryptochrome-4
found in the birds' retinas.
For 20 years, experts have assumed that
this protein acts like a bird's magnetic sensor.
It is microscopic compass that points the bird
in a specific direction.
The protein is involved in chemical
reactions that produce varying amounts of new molecules depending on the
direction of the Earth's magnetic field.
The bird's neurons eventually react to the
amount of these molecules to redirect the animal.
"But no one can confirm or verify this
in the laboratory," said biologist Jingjing Shu of the University of
Oldenburg in Germany.
How the protein reacts to magnetic fields
"How animals perceive magnetic fields
is a mystery.
We don't know much about it. This is
another great Holy Grail in sensory biology."
In a step towards confirmation, Xu's team
has now observed, in detail, how the protein responds to magnetic fields when
isolated in a test tube.
A cryptochrome-4 similar to real birds Crypt-4
The researchers studied the cryptochrome-4
they produce themselves, rather than proteins extracted from real birds.
To make cryptochrome-4, they inserted DNA
instructions for protein production into it.
The bacteria read the instructions and made
the proteins.
"The protein you get from bacteria is
identical to the one found in birds," said biologist Henrik Mouritsen from
the University of Oldenburg.
Chemical reactions of bird cryptochrome-4 in a magnetic field
The team observed the protein undergoing chemical
reactions inside a test tube placed in magnetic fields about a hundred times
stronger from the earth.
By comparing the types of proteins found in
different bird species, they discovered that.:
- Cryptochrome-4 in a migratory European robin is more sensitive to magnetic fields than cryptochrome-4 found in chickens and pigeons, which do not migrate.
In addition, their observations indicated
that cryptochrome-4 could stimulate neural activity - and thus communication
with the bird's brain - through its chemical reactions.
"The [reaction products] It exists
long enough and is produced in sufficient quantities to serve as signaling
material," Warrant said.
The team wanted to better understand how
the protein activates the birds' neurons.
To this end, they simulated the chemical
reactions of cryptochrome-4 on a computer.
These interactions, which change the shape
and structure of the protein, involve the movement of single electrons.
That’s means that we are in the realm of quantum
mechanics.
In these reactions, light strikes and
distorts the protein, which is made up of a series of molecules folded in on
itself.
This distortion causes the electrons in one
part of the chain to jump from one bond to another to form a pair of molecules.
These two molecules have an odd number of
electrons that pair up - leaving one unpaired electron.
Then the two unpaired electrons in each
molecule form a binary, with the quantum spins pointing in opposite directions.
Quantum mechanics comes into play
This is where quantum mechanics comes in.
The spins of the two electrons begin to
oscillate, with one electron tilting in the direction so that their spins line up.
Then back again, about a million times a
second.
When the electron spins are aligned, they
create more feedback reactions for the neurons to respond to than when the
spins are opposite.
The time that the electrons spend in
alignment or not depends on the direction of the magnetic field.
Thus, the response of a bird's neuron
depends on the direction of the magnetic field.
Similar to the way the neurons in our eyes
respond to different wavelengths of light and send information to our brains
that is interpreted as colors.
It is plausible that the neurons in birds
transmit information about magnetic fields - allowing the birds to see the
magnetic fields and to navigate them.
