NASA Baffled by Unexplained Force Acting on Space Probes

Mysteriously, five spacecraft that flew past the Earth have each displayed unexpected anomalies in their motions.

These newfound enigmas join the so-called "Pioneer anomaly" as hints that unexplained forces may appear to act on spacecraft.

A decade ago, after rigorous analyses, anomalies were seen with the identical Pioneer 10 and 11 spacecraft as they hurtled out of the solar system. Both seemed to experience a tiny but unexplained constant acceleration toward the sun.

A host of explanations have been bandied about for the Pioneer anomaly. At times these are rooted in conventional science — perhaps leaks from the spacecraft have affected their trajectories. At times these are rooted in more speculative physics — maybe the law of gravity itself needs to be modified.

Now Jet Propulsion Laboratory astronomer John Anderson and his colleagues — who originally helped uncover the Pioneer anomaly — have discovered that five spacecraft each raced either a tiny bit faster or slower than expected when they flew past the Earth en route to other parts of the solar system.

'Humble and perplexed'

The researchers looked at six deep-space probes — Galileo I and II to Jupiter, the NEAR mission to the asteroid Eros, the Rosetta probe to a comet, Cassini to Saturn, and the MESSENGER craft to Mercury. Each spacecraft flew past the our planet to either gain or lose orbital energy in their quests to reach their eventual targets.

In five of the six flybys, the scientists have confirmed anomalies.

"I am feeling both humble and perplexed by this," said Anderson, who is now working as a retiree. "There is something very strange going on with spacecraft motions. We have no convincing explanation for either the Pioneer anomaly or the flyby anomaly."

In the one probe the researchers did not confirm a noticeable anomaly with, MESSENGER, the spacecraft approached the Earth at about latitude 31 degrees north and receded from the Earth at about latitude 32 degrees south. "This near-perfect symmetry about the equator seemed to result in a very small velocity change, in contrast to the five other flybys," Anderson explained — so small no anomaly could be confirmed.

The five other flybys involved flights whose incoming and outgoing trajectories were asymmetrical with each other in terms of their orientation with Earth's equator.

For instance, the NEAR mission approached Earth at about latitude 20 south and receded from the planet at about latitude 72 south. The spacecraft then seemed to fly 13 millimeters per second faster than expected. While this is just one-millionth of that probe's total velocity, the precision of the velocity measurements was 0.1 millimeters per second, carried out as they were using radio waves bounced off the craft. This suggests the anomaly seen is real — and one needing an explanation.

The fact this effect seems most evident with flybys most asymmetrical with respect to Earth's equator "suggests that the anomaly is related to Earth's rotation," Anderson said.

As to whether these new anomalies are linked with the Pioneer anomaly, "I would be very surprised if we have discovered two independent spacecraft anomalies," Anderson told SPACE.com. "I suspect they are connected, but I really do not know."

Unbound idea

These anomalies might be effects we see with an object possessing a spacecraft's mass, between 660 and 2,200 lbs. (300 and 1,000 kg), Anderson speculated.

"Another thing in common between the Pioneer and these flybys is what you would call an unbound orbit around a central body," Anderson said. "For instance, the Pioneers are flying out of the solar system — they're not bound to their central body, the sun. For the other flybys, the Earth is the central body. These kinds of orbits just don't occur very often in nature — it could be when you get into an unbound orbit around a central body, something goes on that's not in our standard models."

The researchers are now collaborating with German colleagues to search for possible anomalies in the Rosetta probe's second flyby of the Earth on November 13.

"We should continue to monitor spacecraft during Earth flybys. We should look carefully at newly recovered Pioneer data for more evidence of the Pioneer anomaly," Anderson added. "We should think about launching a dedicated mission on an escape trajectory from the solar system, just to look for anomalies in its motion."

Montana State University physicist Ronald Hellings, who did not participate in this study, said, "There's definitely something going on. Whether that's because of new physics or some problem with the model we have is yet to be worked out, as far as I know. A lot of people are trying to look into this."

Anderson and his colleagues will detail their latest findings in an upcoming issue of the journal Physical Review Letters.

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Physicists Successfully Store and Retrieve Nothing

t sounds like a headline from the spoof newspaper The Onion, but for physicists, this is actually an achievement: Two teams have stored nothing in a puff of gas and then retrieved it a split second later. Storing a strange form of vacuum builds on previous efforts in which researchers stopped light in its tracks (ScienceNOW, 22 January 2001) and may mark a significant step toward new quantum information and telecommunication technologies.

To stop light, researchers first shine an intense and continuous beam of laser light into a gas of atoms. That "control beam" tickles the atoms to allow a pulse of laser light of another wavelength to enter the gas. To trap the pulse, researchers turn off the control beam, which causes the pulse to imprint itself on the atoms. To release it again, they turn on the control laser.

So storing a vacuum might sound ridiculously simple: Follow the same procedure but leave out the pulse, and you store nothing. However, Alexander Lvovsky of the University of Calgary in Canada and his colleagues and Mikio Kozuma of the Tokyo Institute of Technology in Japan and his group have stored a very peculiar type of nothingness called a "squeezed vacuum."

To see what this is, begin with a normal light wave. Classically, this is a smooth wave of electromagnetic fields with equally spaced peaks and dips. But throw in quantum mechanics and things get more complicated. The precise height of the wave becomes uncertain, so the wave gets fuzzy (see figure). Physicists have learned how to manipulate that inevitable uncertainty--for example, making it smaller at the peaks and larger in between. That makes "phase-squeezed light." Now imagine turning down the intensity of the phase-squeezed light to zero. The wave itself goes away, but the waxing and waning uncertainty remains, creating a squeezed vacuum.

This is what Lvovsky and Kozuma stored. To make a pulse of squeezed vacuum, both used a device called an optical parametric amplifier, the heart of which is a crystal whose optical properties can be controlled by laser light. Kozuma and colleagues stored pulses of squeezed vacuum for up to 3 microseconds in rubidium atoms chilled to near absolute zero, they report in a paper to be published in Physical Review Letters. Lvovsky and colleagues stored their pulses for 1 microsecond in warm rubidium gas and say they reconstructed the squeezed vacuum in greater detail. Their results will appear in the same journal.

Proving that the squeezed vacuum survived its confinement is tricky, as it's hard to measure nothing. To probe the retrieved vacuum, researchers "mixed" it with the same ordinary laser light that was used to excite the optical parametric amplifier and make the squeezed vacuum. They then observed the telltale up and down in the uncertainty in that light beam, which was effectively transferred from the resurrected vacuum.

"I'm very impressed," says physicist Alexander Kuzmich of the Georgia Institute of Technology in Atlanta. "It's a real technical achievement." The ability to store squeezed states could help pave the way to new types of quantum networks that would carry uncrackable coded messages, says Kuzmich, who in 2006 stored and retrieved a single photon. More conceptually, such experiments might help spell out the boundary between the quantum and classical realms, he says. "There is something we still don't understand about that transition."

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'Northern lights lab' switched on

Aurora observatory opens on remote Arctic island.

SVALBARD For many people, living through the murky twilight of a polar winter would be a depressing experience. But not for the scientists working at a new observatory on the remote Norwegian island of Svalbard. For them, the Arctic darkness gives them the perfect view of the aurora borealis, also known as the northern lights.

These mysterious swirls of light, visible in the polar sky, are caused when superfast particles spat out by the Sun's nuclear inferno hit our atmosphere, causing atoms high in the sky to give off a ghostly glow. These aurorae are only visible in polar regions because the Sun's particles are channelled along the Earth's magnetic field lines, which emerge roughly from Earth's poles. Because they occur at altitudes of more than 80 kilometres, studying them requires very sensitive optical instruments, and a decent vantage-point far from any light pollution.

The new Kjell Henriksen Observatory, perched at the top of the Advent Valley outside Svalbard's largest settlement, Longyearbyen, offers just that. Svalbard provides "a window into space", says Fred Sigernes, an atmospheric researcher at the University Centre in Svalbard, which runs the new observatory. It joins several other facilities that already study the northern lights.

Opened last week by Norway's higher-education minister, Tora Aasland, the new observatory currently houses instruments from 16 institutions in 7 countries. "There are facilities for all sorts of people and instruments," says Dag Lorentzen, also from the University Centren in Svalbard. The instruments are mainly optical, because the aurora borealis gives off visible light.

The observatory will be one of the few places on Svalbard that will be at its busiest during the winter months, says Lorentzen. Though some work has already begun, the main optical telescope will be installed this summer; so the real action will begin next winter, when researchers will be observing the dark skies around the clock.

Northern dark

From late October onwards, Svalbard, at a latitude of about 78º North, is plunged into round-the-clock darkness. Now, in late February, it is only two weeks since the official 'polar dawn', and by mid-morning still only the mountaintops are tinged with the Sun's tentative pinkish rays. Down in Longyearbyen, the light, reflected off the snowy slopes, has an eerie bluish tinge — the town will not see direct sunlight for a few days yet.

The researchers at the observatory have a fairly unorthodox commute to work. The journey from Longyearbyen involves driving along the wide glacial Advent Valley to Mine no. 7 — Svalbard's only still-functioning coal mine. From there, the observatory is reached in army-surplus vehicles, which bump and rumble up the frozen slopes on caterpillar treads.

So sensitive are the instruments at the observatory that visitors are not even allowed to use headlights when driving up the hillside, and all communal areas within the observatory have heavy shutters on their windows.

Once at the observatory, access to the building is currently through the back door, as the main entrance is under 2 metres of snow. But they're prepared for poor weather. They have 10 tonnes of backup batteries for power emergencies, and several rooms full of bunk beds for sleeping in the event of storms. Lorentzen and his colleagues have already done an 18-day stint at the observatory, while waiting for the right conditions to launch a radar rocket into the atmosphere to collect data on the chemicals given off when the aurora lights are produced.

On the day side

Ironically, Svalbard's long polar night will also allow researchers to study what are often referred to as the 'dayside aurora'. The most commonly visible northern lights are the 'nightside aurora', which occur when solar-wind particles are 'slingshotted' around by Earth's magnetic field and enter the atmosphere on the side of Earth facing away from the Sun. That's why northern lights are typically visible at night.

But during the noon darkness of Svalbard's winter, observers should be able to see the dayside aurora, which enter our atmosphere directly. Without the extra slingshot magnetic kick, these particles are less energetic, so produce a fainter, reddish glow.

The observatory's researchers hope that their data could soon help to answer more general questions about solar weather, of which the northern lights are just one side-effect. Large solar storms, which produce spectacular auroral displays, can also knock out communications satellites, force planes to be diverted, and mess up your in-car global positioning system. The Sun is currently in the weakest phase of its 11-year activity cycle — within a few years, such solar flare-ups are set to become more common.

It may even be possible, one day, to harvest the immense energy outbursts behind the northern lights, Lorentzen says, although he admits that currently we have no idea how. "All we know is that it is a lot of energy," he says.

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Physics lab completes world's largest jigsaw puzzle

By Stephanie Nebehay

GENEVA (Reuters) - A 100-tonne wheel, the last piece of an ambitious experiment that scientists hope will help unlock the secrets of the universe, was successfully lowered into an underground cavern on Friday.

It is the final major element in the ATLAS particle detector, the largest of four detectors being hooked up to the world's most powerful particle accelerator which the European Organisation for Nuclear Research (CERN) hopes to start up around the middle of 2008.

"This last piece completes this gigantic puzzle," CERN said in a statement.

The wheel was lowered down a 100-metre shaft and aligned within a millimeter of other detectors at CERN, the world's leading centre for particle research located at a sprawling complex along the Swiss-French border.

The ATLAS detector will measure particles called muons expected to be produced in particle collisions in the accelerator, known as the Large Hadron Collider (LHC).

The LHC will recreate conditions just after the Big Bang, which many scientists believe gave birth to the universe, by colliding two beams of particles at close to the speed of light.

"As particles pass through a magnetic field produced by superconducting magnets, this detector has the ability to accurately track them to the width of a human hair," CERN said.

Experiments at the LHC, which lies in an underground tunnel measuring 17 milesin circumference, should allow physicists to take a big leap on a journey that began with Isaac Newton's law of gravity, it said.

Science has been unable to explain fundamental questions such as how particles acquire mass. The experiments will also probe the mysterious dark matter of the universe and why there is more matter than antimatter.

"Soon the first protons will be smashed together and the secrets of our universe will begin to unravel," CERN said.

CERN spokesman James Gillies said: "We know about 4 percent of the universe. The LHC might teach us about what the remaining 96 percent of the universe is made of, what cosmologists call dark matter."

Once the LHC starts running, it is likely to take a year for "new physics" to emerge, he said. Useful science is expected to continue unfolding for up to 20 years.

Some 10,000 scientists from around the world have worked on the complex apparatus since construction began in 1994.

The majority, some 6,000, are from CERN's 20 European member states although Americans are the largest single nationality (1,000), followed closely by Russians, according to Gillies.

Before the LHC can be started up, some 38,000 tonnes of equipment must be cooled to minus 456 degrees Fahrenheit for the magnets to operate in a superconducting state. This is done using many tonnes of liquid nitrogen and liquid helium.

"That is actually colder than outer space. It is a very big task," Gillies said. "It's essentially how a refrigerator works, it is just an extraordinarily large one and the temperature is incredibly cold."

(Editing by Robert Woodward)

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Earth as You've Never Seen it

Awe-inspiring images of our planet erupting, melting and more

A Collision Created the Andes: The world’s longest mountain range, the Andes, flanks the western coast of South America, which is colliding with the ocean floor. Because the rocks forming the continents are lighter than the oceanic crust, the Andes rise up as the floor of the Pacific Ocean slides beneath South America at a rate of about four inches a year. In this image, the colors reflect altitude. The highest mountains are white, while the black bands along the coast represent the deepening sea. Photo by Various Stallites

For centuries, explorers have risked their lives to reach far-flung corners of the planet. Today, satellites provide incredibly sharp images of nearly every spot on Earth, so anyone can sit back and view hard-to-reach places from the comfort of their own home.

Harvesting data from high-tech sensors on various international satellites, Germany’s space-research agency, DLR, compiled these awe-inspiring and enlightening images of islands, mountains and glaciers across the seven continents. Together they are a record of our planet in action—erupting, melting, colliding, cracking. Here, a look at some of the most impressive satellite images of the past 20 years.

This article was originally published in the inaugural issue of Science Illustrated, a recently launched sister publication of Popular Science. Like what you see? Subscribe today at scienceillustrated.com.

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Why Stars Have Seasons

Have you ever wondered why most star patterns are associated with specific seasons of the year? Just why, for instance, can evening sky watchers in the Northern Hemisphere enjoy Orion the Hunter only during the cold wintry months? During balmy summer evenings it is not Orion, but the stars of Scorpius, the Scorpion, that dominate the southern sky. Spring evenings provide us with a view of the sickle of Leo, the Lion. Yet on fall evenings, it's the Great Square of Pegasus that vies for the stargazer's attention.

The change is subtle. Were we to watch the night sky on any one night from dusk to dawn we would notice certain stars rising from above the eastern horizon in the evening hours. They would sweep across the sky during the night, finally setting beneath the western horizon by dawn. No big deal here, since, after all, the sun does the same thing during the daylight hours. It's caused by Earth's rotation.

But with the passage of time, we would notice something rather puzzling.

Those stars that were low over the western horizon during the early evening hours would, within a matter of a few weeks, disappear entirely from our view, their places being taken up by groups which a few weeks earlier were previously higher up in the sky at sundown. In fact, it would seem that with the passage of time, all the stars gradually shift westward while new stars move up from the eastern horizon to take their places.

But just why is this shift happening?

Four minutes a day

If we were to synchronize our clocks using the motions of the stars as a reference we would discover that the Earth would complete a single turn on its axis not in 24 hours, but actually 23 hours and 56 minutes, or four minutes shy of 24 hours. This would be a day based upon the apparent movement of the stars in our sky, which astronomers call a "sidereal" day from the Latin word for star.

While this is happening, all of us are being carried around the sun on an annual journey almost 600 million miles long. Our orbit is almost a circle and as seen from the sun the Earth would move about one degree each day, since we take about 365 days to go around a circle of 360 degrees. As seen from Earth — from our vantage point — the sun seems to move and it changes its place in the sky by that one-degree per day, as measured against the background of stars.

Of course, we can't see the stars in the daytime but astronomers can measure the position of the sun. The direction of the sun's apparent motion is eastward among the stars. Since the daily turning of the sky (caused by the Earth's rotation) appears to move westward, this slight motion of the sun is what makes a day as measured by the sun (called a solar day) longer: the Earth must turn about one degree (or about 4 minutes) more than a full circle to complete a 24-hour day as measured by the sun.

That slight shift each day is what makes the different stars and constellations appear at different times of the year. The sun slowly changes its position, but so slowly that the stars which are up when the sun is down also change.

If you want to try an experiment, look outside some clear evening from a location you can find again. Notice the exact time that a particular star is directly aligned with some object, like a telephone pole or a roof. Look the very next night; stand in the very same place and the star will be there four minutes before the time it was the previous night (of course your clock must be set accurately each night).

You are observing the effects of the Earth's motion around the sun.

Star time versus sun time

At this point you might be a bit confused. If the Earth takes 23 hours 56 minutes to turn on its axis, why do we say that a day is 24 hours long?

Astronomers have devised special clocks adjusted to keep time solely by the stars. These astronomical clocks keep sidereal time. There is no a.m. or p.m. in a sidereal day.

With the clocks that we use every day, the hour hand goes completely around 12 hours twice a day. But with a sidereal clock, there are 24 hourly numbers on the dial instead of 12 and the hour hand goes around only once in a sidereal day. The hours start at 00 hour (zero hour) and are numbered straight through to 23 hours and then starts at the zero hour again. The other difference is that the sidereal clock runs four minutes fast as compared to a regular clock.

Now, if our daily lives were governed by the sidereal clock, there would be times during the year when the sun would appear highest in the sky at noontime, but at other times of the year it would appear highest at midnight or setting at 6 a.m. (or something else strange). We're accustomed, of course, to being awake when it's light and asleep when it's dark, so astronomers also have developed a "mean" sun — which is fictitious and for most of the year deviates somewhat from the sun's actual position in the sky.

Yet, the mean sun governs our ordinary clocks and results in the 24-hour time scale of which we have become accustomed to all of our lives.

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Spacecraft at Mars Prepare to Welcome New Kid on the Block

Three Mars spacecraft are adjusting their orbits to be over the right place at the right time to listen to NASA's Phoenix Mars Lander as it enters the Martian atmosphere on May 25.

Every landing on Mars is difficult. Having three orbiters track Phoenix as it streaks through Mars' atmosphere will set a new standard for coverage of critical events during a robotic landing. The data stream from Phoenix will be relayed to Earth throughout the spacecraft's entry, descent and landing events. If all goes well, the flow of information will continue for one minute after touchdown.

"We will have diagnostic information from the top of the atmosphere to the ground that will give us insight into the landing sequence," said David Spencer of NASA's Jet Propulsion Laboratory, Pasadena, Calif., deputy project manager for the Phoenix Mars Lander project. This information would be valuable in the event of a problem with the landing and has the potential to benefit the design of future landers.

Bob Mase, mission manager at JPL for NASA's Mars Odyssey orbiter, said, "We have been precisely managing the trajectory to position Odyssey overhead when Phoenix arrives, to ensure we are ready for communications. Without those adjustments, we would be almost exactly on the opposite side of the planet when Phoenix arrives."

NASA's Mars Reconnaissance Orbiter is making adjustments in bigger increments, with one firing of thrusters on Feb. 6 and at least one more planned in April. The European Space Agency's Mars Express orbiter has also maneuvered to be in place to record transmissions from Phoenix during the landing. Even the NASA rovers Spirit and Opportunity have been aiding preparations, simulating transmissions from Phoenix for tests with the orbiters.

Launched on Aug. 4, 2007, Phoenix will land farther north than any previous mission to Mars, at a site expected to have frozen water mixed with soil just below the surface. The lander will use a robotic arm to put samples of soil and ice into laboratory instruments. One goal is to study whether the site has ever had conditions favorable for supporting microbial life.

Phoenix will hit the top of the Martian atmosphere at 5.7 kilometers per second (12,750 miles per hour). In the next seven minutes, it will use heat-shield friction, a parachute, then descent rockets to slow to about 2.4 meters per second (5.4 mph) before landing on three legs.

Odyssey will tilt from its normally downward-looking orientation to turn its ultrahigh-frequency (UHF) antenna toward the descending Phoenix. As Odyssey receives a stream of information from Phoenix, it will immediately relay the stream to Earth with a more capable high-gain antenna. The other two orbiters, Mars Reconnaissance Orbiter and Mars Express, will record transmissions from Phoenix during the descent, as backup to ensure that all data is captured, then transmit the whole files to Earth after the landing. "We will begin recording about 10 minutes before the landing," said JPL's Ben Jai, mission manager for Mars Reconnaissance Orbiter.

The orbiters' advance support for the Phoenix mission also includes examination of potential landing sites, which is continuing. After landing, the support will include relaying communication between Phoenix and Earth during the three months that Phoenix is scheduled to operate on the surface. Additionally, NASA and European Space Agency ground stations are performing measurements to determine the trajectory of Phoenix with high precision.

With about 160 million kilometers (100 million miles) still to fly as of late February, Phoenix continues to carry out testing and other preparations of its instruments. The pressure and temperature sensors of the meteorological station provided by the Canadian Space Agency were calibrated Feb. 27 for the final time before landing. "The spacecraft has been behaving so well that we have been able to focus much of the team's attention on preparations for landing and surface operations," Spencer said.

The Phoenix mission is led by Peter Smith of the University of Arizona, Tucson, with project management at JPL and development partnership at Lockheed Martin, Denver. International contributions are provided by the Canadian Space Agency; the University of Neuchatel, Switzerland; the universities of Copenhagen and Aarhus, Denmark; the Max Planck Institute, Germany; and the Finnish Meteorological Institute. Additional information on Phoenix is online at http://www.nasa.gov/phoenix and http://phoenix.lpl.arizona.edu . JPL, a division of the California Institute of Technology in Pasadena, manages Mars Odyssey and Mars Reconnaissance Orbiter for the NASA Science Mission Directorate, Washington. Additional information on NASA's Mars program is online at http://www.nasa.gov/mars .

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Researchers discover gene that blocks HIV

A team of researchers at the University of Alberta has discovered a gene that is able to block HIV, and in turn prevent the onset of AIDS.

Stephen Barr, a molecular virologist in the Department of Medical Microbiology and Immunology, says his team has identified a gene called TRIM22 that can block HIV infection in a cell culture by preventing the assembly of the virus.

"When we put this gene in cells, it prevents the assembly of the HIV virus," said Barr, a postdoctoral fellow. "This means the virus cannot get out of the cells to infect other cells, thereby blocking the spread of the virus."

Barr and his team also prevented cells from turning on TRIM22 - provoking an interesting phenomenon: the normal response of interferon, a protein that co-ordinates attacks against viral infections, became useless at blocking HIV infection.

"This means that TRIM22 is an essential part of our body's ability to fight off HIV. The results are very exciting because they show that our bodies have a gene that is capable of stopping the spread of HIV."

One of the greatest challenges in battling HIV is the virus' ability to mutate and evade medications. Antiretroviral drugs introduced during the late 1990s interfere with HIV's ability to produce new copies of itself - and even they are beneficial, the drugs are unable to eradicate the virus. Barr and his team have discovered a gene that could potentially do the job naturally.

"There are always newly emerging drug-resistant strains of HIV so the push has been to develop more natural means of blocking the virus. The discovery of this gene, which is natural in our cells, might provide a different avenue," said Barr. "The gene prevents the assembly of the virus so in the future the idea would be to develop drugs or vaccines that can mimic the effects of this gene."

"We are currently trying to figure out why this gene does not work in people infected with HIV and if there is a way to turn this gene on in those individuals," he added. "We hope that our research will lead to the design of new drugs, or vaccines that can halt the person-to-person transmission of HIV and the spread of the virus in the body, thereby blocking the onset of AIDS."

The researchers are now investigating the gene's ability to battle other viruses.

Barr's research is funded by the Canadian Institutes of Health Research, the Natural Sciences and Engineering Research Council and the Alberta Heritage Foundation for Medical Research. The findings are published in the Public Library of Science Pathogens.

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First Peek Into Deepest Recesses Of Human Brain

The scientists believe they may be opening the door to inquiries into a region that acts as the staging area for the brain chemicals whose overabundance or absence in other parts of the brain are at the root of many neuropsychiatric disorders, like addiction, schizophrenia and Parkinson's disease.

Reporting in the Feb. 28 edition of Science, the scientists describe using functional magnetic resonance imaging to study brainstem activity in dehydrated humans. The scanning technique allows researchers to watch the brain in action.

The subjects were participating in classical conditioning experiments in which they were presented with a visual clue, then, at varying intervals, given a drink. The researchers were able to track changes in blood flow in areas of the brainstem associated with enhanced activity of the brain chemical dopamine -- as the person experienced either pleasure or disappointment at receiving or not receiving the reward.

"For a long time, scientists have tried looking at this area of the brain and have been unsuccessful -- it's just too small," said Kimberlee D'Ardenne, the lead author on the paper. Until now, scientists wanting to use brain scans to study brain chemicals like dopamine were relegated to watching its effects in other more accessible parts of the brain, like the prefrontal cortex and ventral striatum. However, this was downstream of its source, and therefore possibly much less accurate, D'Ardenne said.

"We wanted to try because the brainstem is so important to activities in the rest of the brain," said D'Ardenne, a postdoctoral student in the Department of Chemistry. "We believe it could be a key to understanding all kinds of important behavior."

For the research, D'Ardenne collaborated with Jonathan Cohen, co-director of the Princeton Neuroscience Institute, and Samuel McClure and Leigh Nystrom, other institute scientists. They conducted the studies on the University's own brain scanner located on campus in Green Hall.

Cohen noted that these findings provide a critical link between studies in non-human animals that have looked directly at the activity of dopamine cells in the brainstem and studies in humans of behaviors thought to be related to dopamine. "It could also open up entirely new avenues of study," he said.

The team was able to develop high-resolution images that tracked the activity of tiny clusters of dopamine neurons. They weeded out distortions caused by many pulsing blood vessels in the brainstem. They also employed computerized rules of thumb known as algorithms and imaging techniques to reduce the effects of head movement and combine images from different subjects.

The MRI device produces three-dimensional images that show what portions of the brain engage during actions and thought processes. This allows the investigators to correlate physical processes with mental activities with unprecedented precision.

The brain stem, a tiny, root-shaped structure, is the lower part of the brain and sits atop the spinal cord. The area controls brain functions necessary for survival, such as breathing, digestion, heart rate, blood pressure and arousal. The brain structure also serves as the home base for the brain chemicals, also known as neuromodulators, such as dopamine, serotonin and norepinephrine. The chemicals spring forth into other brain regions from there, zipping along routes called axons.

The team's experiments confirmed results already seen in animal studies. Blood flow increased in dopamine centers of the brainstem when test subjects were happily surprised with a reward. However, there was no activity when participants received less than what they expected, a finding that is different from the results of previous studies looking farther downstream.

"We are just at the beginning of understanding these crucial pathways," D'Ardenne said. "But it gives us a hint about what is possible to know."

The tiny clumps of cells containing neuromodulator chemicals in the brainstem, called nuclei, have long been known to play a critical role in the regulation of brain function, and disturbances of these systems have been implicated in most psychiatric disorders, from addiction to schizophrenia, D'Ardenne said.

The Princeton group wants to understand how the brain's physical structures give rise to the functions of the mind, a field known as cognitive neuroscience.

For years, neuroscientists focused on the brain while psychologists dealt with the mind. The new field combines both and is being powered by scientific advances in brain imaging and gene manipulation that allows researchers to record and measure the activity of brain cells as humans or animals perform mental tasks.

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