I completely missed the Nobel award in biology yesterday, but I see that one has been awarded this morning in physics. The former involves three scientists, the latter a lone physicist.
The Medicine or Physiology prize release is here. It describes advances in “optogenetics,” the use of optical signals to detect how neurons work. It’s very clever, based on an algal protein, rhodopsin, that is activated by light and, when put in a nerve cell, will create an impulse when the cell is illuminated by blue light.
There’s a clear discussion of the Prize-winning research at The Conversation (click below to read):
A summary:
Scientists who worked out how to control brain cells with light have won this year’s Nobel prize in physiology or medicine. Karl Deisseroth, Peter Hegemann and Georg Nagel were honoured for their research into “light-gated ion channels and optogenetics”.
Peter Hegemann, at Humboldt University of Berlin, and Georg Nagel, at the University of Würzburg, wanted to understand how a tiny, single-celled alga called Chlamydomonas senses light. Light-sensing is not unique to animals with eyes: organisms throughout the living world use light to detect their surroundings and respond to changes in their environment. Even single-cell organisms have proteins that respond to light. These proteins are used to move towards or away from light, to generate energy and to respond to the various demands of a 24-hour day.
Hegemann and Nagel discovered that Chlamydomonas has a beautifully ingenious mechanism of light detection that relies on a single protein called channelrhodopsin.
Channelrhodopsin is built into the outer membrane of the algal cell. Part of the protein faces the water outside the cell and part faces the inside. The protein also contains a small molecule called retinaldehyde, which is able to absorb light.
When light hits the retinaldehyde inside channelrhodopsin, it changes shape. This makes the channelrhodopsin protein change shape too. That change opens a tiny passage through the cell membrane. Positively charged particles, including sodium, can then flow from the water outside the alga into the cell. This movement of charged particles sends a signal inside the alga that helps it swim.
The researchers realised that if they could put channelrhodopsin into nerve cells, they might be able to switch those cells on simply by shining a light on them. That is exactly what Hegemann, Nagel and the third Nobel-prize winner, Karl Deisseroth, a psychiatrist and bioengineer at Stanford University in California, went on to do.
. . . and how it’s used, with a cool example:
The ability to control nerve cells with light is called optogenetics. It has become a powerful research tool because scientists can use it to switch specific groups of nerve cells on and off and see what happens.
First, scientists deliver the gene for channelrhodopsin to the nerve cells they want to study. The gene is usually carried into the cells by a virus that has been altered so that it cannot cause disease. The cells then make the channelrhodopsin protein, which makes them respond to light.
In animals such as mice, scientists can shine light into the brain through a thin optical fibre. When the light reaches the cells, channelrhodopsin opens and the cells become active. Nearby nerve cells that do not contain the protein are unaffected.
Light can be aimed at a very small part of the brain and switched on and off extremely quickly. This makes optogenetics a powerful way to investigate how the brain works. For example, if scientists want to know whether a particular group of nerve cells is involved in memory, sleep, sensation or movement, say, they can switch those cells on with light and see what happens.
In one experiment in 2012, a team at the Massachusetts Institute of Technology gave mice a mild electric shock in a particular cage. They used optogenetics to tag the nerve cells in the brain’s memory centre that were active during that the fear-conditioning experiment. Days later, in a different cage, they switched those cells on with light. The mice froze in fear, as if they remembered the shock.
Mice that were not shocked did not freeze, which showed that the light was reactivating a specific memory. Deisseroth was one of the study’s authors.
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And the press release for the physics prize is here. An excerpt:
Francis Halzen realised that ice at the South Pole could be used to track particles known as neutrinos. His vision and scientific leadership have been fundamental for the IceCube Neutrino Observatory – a cubic kilometre of ice that is equipped with light sensors. Using IceCube, researchers can capture neutrinos from extremely energy-rich processes in the distant universe.
Neutrinos are everywhere, but they do not make themselves known. They pass all the way through the Earth and through our bodies without us noticing. Very rarely, a single neutrino will interact with an atomic nucleus, which makes it possible for someone with the right equipment to discover them.
Scientists have long known that the cosmos contains natural particle accelerators, which fire out particles with energies up to a million times more than can be achieved in laboratories on Earth. Much about these sources is mysterious: what are they, where are they, and what are the main processes inside them?
Neutrinos with extremely high energies are created in the same environments as other types of particles. However, unlike other particles, neutrinos reach us without changing direction or losing energy. This means they can provide information that is not available in any other way.
Francis Halzen first presented his vision for capturing neutrinos at the South Pole in 1988. When a neutrino collides with an atomic nucleus, it produces a flash of light that can be tracked by sensors in the clear glacial ice. The South Pole’s ice has many advantages, as it is free from various types of interference and the area is geologically stable, with no earthquakes. Halzen and his idea soon gained the support of other researchers and, just a few years later, preliminary testing was conducted on sensors in ice.
Cosmic neutrinos with extremely high energies are very rare, so an enormous volume of ice is needed to observe an adequate number of collisions. IceCube covers an entire cubic kilometre and was finished in 2011. Researchers soon discovered the first high-energy neutrinos and, a few years later, could publish their discovery of neutrinos that must originate far outside our solar system. The search for the universe’s neutrino sources could begin in earnest.
“Francis Halzen has led an international team of researchers and engineers who have provided us with a fantastic instrument. His tenacity and scientific vision has paved the way for a new kind of astronomy,” says Mark Pearce, Chair of the Nobel Committee for Physics.
The neutrino interactions that are continuously collected by IceCube will provide researchers with novel knowledge about the violent settings in which high-energy neutrinos can be created – and could even reveal previously unknown cosmic phenomena.
Here’s the apparatus and how it works, taken from the Nobel Prize press release. See if you can read it by clicking to enlarge. The observed ice and detectors are buried way underground. Just getting this damn thing set up at the South Pole would merit a prize by itself!
Now perhaps some reader with expertise can tell us in the comments why high-energy neutrinos from outside the solar system are so important compared to lower-energy neutrinos from, say, the Sun.
