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21 July 2016

Perspectives on the cosmos: Habitable planets, brain maps, photons & the universe

A New Map of the Brain Redraws the Boundaries of Neuroscience

A new brain map, based on multiple scans of more than 400 individuals, has carved the "cortex" into 180 different compartments - 97 of which are new.

This crumpled outer layer of the brain is home to our advanced cognition, perception and movement.

It has been mapped in various ways for centuries, but this new effort is a landmark attempt at a definitive, modern atlas for neuroscientists.

The work is reported in Nature and the data is available to scientists online.

It the most significant result to date from the Human Connectome Project, a US-led collaboration aimed at unravelling the wiring of the human brain and how it affects behaviour.

'Mammoth effort'

Dr Emma Robinson, now at Imperial College London, is a co-author of the Nature paper and was part of the Oxford University team which built software to analyse the project's huge streams of data.

"This is the culmination of the entire HCP project that we've been working towards," she told BBC News.

"This paper is really a mammoth effort by Matthew Glasser and David Van Essen (of Washington University in St Louis, Missouri) - manually labelling brain regions, but also pulling together all the streams that we've been working on, trying to collect incredibly high quality images and state of the art imaging processing techniques."

The team used several different types of information, derived from lengthy scanning sessions of 210 people, to define the boundaries of 180 areas in each brain hemisphere.

To begin with, there were physical properties to consider - such as the amount of myelin, the substance which wraps nerve fibres, detected throughout the cortex; or variations in the folding and the thickness of the cortex.

But the researchers also looked at brain activity. Which regions were activated by particular tasks - reading as opposed to gambling, for example? And to what extent was activity in one area correlated and coordinated with activity elsewhere?

After using automatic computational tools to separate those 180 areas, the team set about testing and confirming the results on a fresh sample of 210 individual brains.

There were, perhaps inevitably, some differences between individuals, but brain researcher have welcomed the map as the most detailed human brain atlas to date.

Prof Tim Behrens, another computational neuroscientist at the University of Oxford, is involved in the HCP but was not an author on the new paper - which he described as "awe inspiring".

"Obviously there are a bunch of people who have done parcellations before. But this one is extraordinary because of the level of precision.

"Every one of those 180 areas in this paper is described in detail - its relation to the previous literature, its functional properties, its anatomical properties... Nobody will do as good a job as this for a long time.

"It will now be the parcellation that is used by all of neuroscience, I would think."

Prof Simon Eickhoff studies brain organisation at the University of Dusseldorf in Germany and was not involved in the research.

He told the BBC the new map was "a really big step forward" and was built on an impressive variety of data.

"It's very useful. It betters the descriptions that have been available up till now," Prof Eickhoff said.

But he cautioned against describing the 97 freshly delineated regions as "new areas".

"If you look at the classical brain maps, even from the 19th century - they were whole-brain maps; they had a label for every spot on the cortex. Any part of the brain has already been looked at.

"[This work] certainly defines something clearly, where knowledge has been imprecise and maybe contradictory. But 'new' is a tricky term."

Prof Behrens, meanwhile, said that beyond the map's utility for neuroscientists and neurosurgeons, it would change the way he thinks about the human brain.

"It conceptually changes things. Brain areas are not coarsely divided with, say, 50 pieces that we need to figure out what they're doing.

"As you get more and better data, you can subdivide it further and further - and we should be thinking about the brain in this much more granular way."


2 'Nearby' Exoplanets Confirmed to Be Rocky — and May Be Habitable

On May 2, scientists from MIT, the University of Liège, and elsewhere announced they had discovered a planetary system, a mere 40 light years from Earth, that hosts three potentially habitable, Earth-sized worlds. Judging from the size and temperature of the planets, the researchers determined that regions of each planet may be suitable for life.

Now, in a paper published today in Nature, that same group reports that the two innermost planets in the system are primarily rocky, unlike gas giants such as Jupiter. The findings further strengthen the case that these planets may indeed be habitable. The researchers also determined that the atmospheres of both planets are likely not large and diffuse, like that of the Jupiter, but instead compact, similar to the atmospheres of Earth, Venus, and Mars.

The scientists, led by first author Julien de Wit, a postdoc in MIT's Department of Earth, Atmospheric and Planetary Sciences, came to their conclusion after making a preliminary screening of the planets' atmospheres, just days after announcing the discovery of the planetary system.

On May 4, the team commandeered NASA's Hubble Space Telescope and pointed it at the system's star, TRAPPIST-1, to catch a rare event: a double transit, the moment when two planets almost simultaneously pass in front of their star. The researchers realized the planets would transit just two weeks before the event, thanks to refined estimates of the planets' orbital configuration, made by NASA's Spitzer Space Telescope, which had already started to observe the TRAPPIST-1 system.

"We thought, maybe we could see if people at Hubble would give us time to do this observation, so we wrote the proposal in less than 24 hours, sent it out, and it was reviewed immediately," de Wit recalls. "Now for the first time we have spectroscopic observations of a double transit, which allows us to get insight on the atmosphere of both planets at the same time."

Using Hubble, the team recorded a combined transmission spectrum of TRAPPIST-1b and c, meaning that as first one planet then the other crossed in front of the star, they were able to measure the changes in wavelength as the amount of starlight dipped with each transit.

"The data turned out to be pristine, absolutely perfect, and the observations were the best that we could have expected," de Wit says. "The force was certainly with us."

A rocky sign

The dips in starlight were observed over a narrow range of wavelengths that turned out not to vary much over that range. If the dips had varied significantly, de Wit says, such a signal would have demonstrated the planets have light, large, and puffy atmospheres, similar to that of the gas giant Jupiter.

But that's not the case. Instead, the data suggest that both transiting planets have more compact atmospheres, similar to those of rocky planets such as Earth, Venus, and Mars.

"Now we can say that these planets are rocky. Now the question is, what kind of atmosphere do they have?" de Wit says. "The plausible scenarios include something like Venus, where the atmosphere is dominated by carbon dioxide, or an Earth-like atmosphere with heavy clouds, or even something like Mars with a depleted atmosphere. The next step is to try to disentangle all these possible scenarios that exist for these terrestrial planets."

More eyes on the sky

The scientists are now working to establish more telescopes on the ground to probe this planetary system further, as well as to discover other similar systems. The planetary system's star, TRAPPIST-1, is known as an ultracool dwarf star, a type of star that is typically much cooler than the sun, emitting radiation in the infrared rather than the visible spectrum.

De Wit's colleagues from the University of Liège came up with the idea to look for planets around such stars, as they are much fainter than typical stars and their starlight would not overpower the signal from planets themselves.

The researchers discovered the TRAPPIST-1 planetary system using TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope), a new kind of ground telescope designed to survey the sky in infrared. TRAPPIST was built as a 60-centimeter prototype to monitor the 70 brightest dwarf stars in the southern sky. Now, the researchers have formed a consortium, called SPECULOOS (Search for habitable Planets Eclipsing ULtra-cOOl Stars), and are building four larger versions of the telescope in Chile, to focus on the brightest ultracool dwarf stars in the skies over the southern hemisphere. The researchers are also trying to raise money to build telescopes in the northern sky.

"Each telescope is about $400,000—about the price of an apartment in Cambridge," de Wit says.

If the scientists can train more TRAPPIST-like telescopes on the skies, de Wit says, the telescopes may serve as relatively affordable "prescreening tools." That is, scientists may use them to identify candidate planets that just might be habitable, then follow up with more detailed observations using powerful telescopes such as Hubble and NASA's James Webb Telescope, which is scheduled to launch in October 2018.

"With more observations using Hubble, and further down the road with James Webb, we can know not only what kind of atmosphere planets like TRAPPIST-1 have, but also what is within these atmospheres," de Wit says. "And that's very exciting."


Human Eye Can Detect Even Individual Photons, The Smallest Unit Of Light: Study

Just how dark does it have to be before our eyes stop working? Research by a team from Rockefeller University and the Research Institute of Molecular Pathology in Austria has shown that humans can detect the presence of a single photon, the smallest measurable unit of light. Previous studies had established that human subjects acclimated to the dark were capable only of reporting flashes of five to seven photons.

The work was led by Alipasha Vaziri, associate professor and head of the Laboratory of Neurotechnology and Biophysics at Rockefeller and an adjunct investigator at the Research Institute of Molecular Pathology. It is published this week in Nature Communications.

Remarkable precision

"If you imagine this, it is remarkable: a photon, the smallest physical entity with quantum properties of which light consists, is interacting with a biological system consisting of billions of cells, all in a warm and wet environment," says Vaziri. "The response that the photon generates survives all the way to the level of our awareness despite the ubiquitous background noise. Any man-made detector would need to be cooled and isolated from noise to behave the same way."

In addition to recording the ability of the human eye to register a single photon, the researchers found that the probability of doing so was enhanced when a second photon was flashed a few seconds earlier, as if one photon "primes" the system to register the next.

A quantum light source

Previous experiments designed to test the human eye's sensitivity have suffered from a lack of appropriate technology, Vaziri says. "It is not trivial to design states of light that contain exactly one or any other number of photons," he says. "This is because the number of photons in a classical light source such as that from a lamp or a laser follow certain statistical distributions. Although you can attenuate the light to reduce the number of photons, you typically can't determine an exact number."

Vaziri's team built a light setup, often used in quantum optics and quantum information studies, called spontaneous parametric down-conversion, or SPDC, which uses a process in which a high-energy photon decays in a non-linear crystal. The process generates exactly two photons with complementary colors. In the experimental setup, one of the photons was sent to the subject's eye while the other was sent to a detector, allowing the scientists to keep track of when each photon was transmitted to the eye.

First evidence

To arrive at their findings, Vaziri and his collaborators combined the light source with, an unprecedented psychophysics protocol called two-alternative forced-choice (2AFC) in which subjects are repeatedly asked to choose between two time intervals, one of which contains a single photon while the other one is a blank. The gathered data from more than 30,000 trials demonstrated that humans can indeed detect a single photon incident on their eye with a probability significantly above chance.

"What we want to know next is how does a biological system achieve such sensitivity? How does it achieve this in the presence of noise? Is the mechanism unique to vision or could it tell us something more general on how other systems could have evolved to detect weak signals in the presence of noise?" says Vaziri.


There are 1.2 million galaxies in this 3D map of the Universe

It took hundreds of physicists and astronomers five years to construct this image, which is the largest-ever, most precise, three-dimensional map of distant galaxies that charts the dark energy propelling the accelerated expansion of the Universe.

Project co-leader Jeremy Tinker from New York University said: "We have spent five years collecting measurements of 1.2 million galaxies over one quarter of the sky to map out the structure of the Universe over a volume of 650 cubic billion light years."

The results of the project have been published in the Monthly Notices of the Royal Astronomical Society. "This map has allowed us to make the best measurements yet of the effects of dark energy in the expansion of the Universe. We are making our results and map available to the world," Tinker adds.

Consistent with the calculations of general relativity, the galaxies were observed drifting towards areas of the Universe with more matter - thus more gravitational pull.

Shirley Ho, an astrophysicist at Berkeley Lab and Carnegie Mellon University (CMU) who co-led two of the companion papers says the data they gathered will pave the way towards more accurate measurements: "We can now measure how much the galaxies and stars cluster together as a function of time to such an accuracy we can test General Relativity at cosmological scales," she said.

On top of the fact that we currently do not know what exactly dark energy and dark matter are, the team also had to decipher between the two in their measurements. Thanks to the Baryon Oscillation Spectroscopic Survey (BOSS) program of the Sloan Digital Sky Survey-III, measurement of the rate at which the Universe expands was made possible, which led them to measure the amount of dark matter and dark energy which our present Universe is made of.

By determining the size of the baryonic acoustic oscillations (BAO) in the three-dimensional distribution of galaxies, BOSS can measure the expansion rate of the Universe. Galaxy distribution was measured starting from 13.7996 billion years ago, 400,000 years from the time the Universe is believed to have started — a time when pressure waves are known to have travelled throughout the cosmos.

From that point on, astronomers were able to observe the competition between dark matter and dark energy in controlling the Universe’s expansion.

"We’ve made the largest map for studying the 95 percent of the Universe that is dark," said David Schlegel, astrophysicist at Lawrence Berkeley National Laboratory (Berkeley Lab) and principal investigator for BOSS.

"In this map, we can see galaxies being gravitationally pulled towards other galaxies by dark matter. And on much larger scales, we see the effect of dark energy ripping the Universe apart."

Rita Tojeiro of the University of St Andrews in Scotland, who co-led the BOSS galaxy clustering working group alongside Tinker outlines how this is a milestone for cosmology:

"We see a dramatic connection between the sound wave imprints seen in the cosmic microwave background 400,000 years after the Big Bang Seed to the clustering of galaxies 7-12 billion years later. The ability to observe a single well-modelled physical effect from recombination until today is a great boon for cosmology."

"The results from BOSS provide a solid foundation for even more precise future BAO measurements, such as those we expect from the Dark Energy Spectroscopic Instrument (DESI)," said Natalie Roe, Physics Division director at Berkeley Lab.

"DESI will construct a more detailed three-dimensional map in a volume of space ten times larger to precisely characterise dark energy — and ultimately the future of our Universe."