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.
I haven’t yet tried to study the physics Nobel Prize in any technical detail. But as I understand it, Halzen’s new detection methods won’t tell us new things about neutrinos as particles, but rather about the processes that produce high energy neutrinos. The idea is that we can now do more extensive “neutrino astronomy”. Studying the flux of high energy neutrinos produced by the big bang and early in the universe, as opposed to the lower energy neutrinos emitted by stars, gives us insight into the big bang and the very early history of the universe. Besides the early universe, it is also thought that recent rare high energy cosmic events such as neutron star collisions produce high energy neutrons that can be detected by Halzen’s methods.
These are both next-level, crazy clever stuff. We humans are so impressive. I mean, collectively, in the sense that some of us are so impressive. How weird and wonderful.
Ditto. Fascinating and, in Jerry’s summation, quite comprehensible without mental strain for this non-scientist.
Edit: thanks Christian and Coel for your further explanations.
I will just reiterate Jerry’s final paragraph asking for some physics expertise from reader(s) on why these extreme energy neutrinos are important…do they confirm or rule out any particular theory? What does their extremely high energy compared with those from our Sun tell us? Or is it just a basic result that we have now seen these in the lab?
What does their extremely high energy compared with those from our Sun tell us?
For one, they tell us where they come form. They originated in “particle accelerators” very far away (thanks Ceiling Cat) but unlike charged particles (e.g. ultra-high-energy protons, which most likely have the same kind of source) their trajectories don’t get bend by magnetic fields.
Since they travel through a lot of space (billions of light years), physicists could gather information on the properties of spacetime at a quantum level (how smooth or “grainy” it is).
Well, this is just off the top of my head. Maybe there’s a lot more that particle physicists can squeeze out of them.
The processes that produce neutrinos in the sun are pretty well understood. Indeed at that sort of energy (MeV), pretty much all of particle physics is pretty well understood, in the sense that we have a good model (the “standard model” of particle physics) that predicts all that behaviour, and no observations at such energies are out of line with the model.
The ultra-high energy neutrinos are up to a billion times more energetic (PeV energies). We don’t know how they are produced or which astrophysical scenarios produce them. They are also more energetic than any particles we can produce in particle accelerators such as at CERN (which go up to 10 TeV). That all means that there is potential to explore new energy ranges and discover new physics.
The current models of fundamental physics are a victim of their own success in that no earthly-laboratory evidence is inconsistent with them, and thus we lack empirical clues to improve the models. The only way to try to “break” the models is to move to very high energies, or to the very large scale (e.g. dark matter, dark energy) or very high gravitational fields (e.g. black holes) or to very rare instances (e.g. the recent possible detection of a dark-matter particle). The ultra-high-energy neutrinos are one potential avenue for doing this.
Excellent. Thanks, Coel.
My gosh these guys are so brilliant and clever!
Many of us have been expecting the prize for optogenetics for several years, wondering how long it would take. The work really did revolutionize neuroscience, and led to the answers to several important questions.
However.. the Nobel is limited to only 3 recipients. And it was a fourth guy, Ed Boyden, working with Deisseroth, who is just as deserving as the other three. Note that I am not saying that he is more deserving; I would not want to make that call. Someone had to be excluded, and, for whatever reason, he drew the short straw. I expect that Deisseroth, in his acceptance speech, will say something about Boyden’s contribution. Deisseroth is that kind of person.
It would sure be nice if they could get rid of that maximum 3 rule. This is really a case where an equally deserving person was left out.
According to Le Monde, Francis Crick had suggested something like this in 1962. They report him as having said that to progress in the study of the brain, we would have to “light up” and “turn off” neurons on demand, adding that “the ideal signal would be light.” (My translation from Le Monde’s translation, so that may have lost something of the original…)
I asked an expert about this (Matthew Cobb), who replied, “With a quick google, it appears that the Le Monde people have been misread the Nobel website, which says that Crick came up with the idea and has (Nobel 1962) after his name. He may have mentioned it in his 1979 Sci Am article, which Diesseroth says was very influential.”
Aha. So Le Monde is not entirely trustworthy either. Good to know.