How the Brain Maps Symbols to Numbers

How the Brain Maps Symbols to Numbers

New research shows the prefrontal cortex handles the work of associating numerals with matching quantities

	NUMBERS ON THE BRAIN:  Scientists say the prefrontal cortex is responsible for making semantic connections between numerical quantities and the symbols that depict them.

In a study that involved teaching monkeys to associate Arabic numerals with their corresponding quantities, German researchers fingered the prefrontal cortex as the part of the mammalian brain that is responsible for relating symbols with abstract concepts.

The finding was surprising to the Andreas Nieder, head of the Primate NeuroCognition Laboratory at the University of Tübingen, and his graduate student Ilka Diester, who figured that the intraparietal sulcus, a lateral region in the rear brain, handled this task. 

"In verbally counting humans, the parietal cortex seems to be the key structure for symbolic number representations," Nieder says, about the study result is published this week in PLoS Biology. "Damage to certain parts of the parietal lobe in humans can elicit very specific deficits in dealing with numbers."

Instead, researchers discovered that the semantic associations are made in the prefrontal part of the cortex (the brain's central processing area), indicating that this region in children and monkeys is involved in the early learning of numeric links—such as that between the numeral 4 with the quantity of four dots—and that the parietal region takes over the job in teens as the associations become more automatic. In fact, imaging studies of children have shown that their prefrontal areas are heavily engaged when drawing connections between symbols and concepts.

Nieder and Diester trained two rhesus monkeys for their experiment. First, they taught the animals to discriminate between different quantities by showing them sets of dots and having them pluck out the ones with equal numbers of dots (from one to four) on them. They then spent several months linking each set of dots to different Arabic numerals.

Following the lessons, the researchers gave the monkeys performance tests during which they were trained to pull a lever when a numeral and its matching number of dots appeared before them. The monkeys made the correct association nearly 90 percent of the time. As the animals mulled their options, researchers scanned 692 randomly selected neurons in the prefrontal cortex and 437 nerve cells in the parietal cortex. The researchers found that 23 percent of the prefrontal neurons showed increased activity during the task, but only 2 percent of the parietal neurons responded.

In addition, groups of neurons in the prefrontal cortex appeared to be tuned to certain amounts, with subsets of the cells responding to specific numerals or quantities: some to 1, others to 2 (and so on). In addition, if a monkey was about to make an incorrect decision, Nieder notes, the researchers observed a very different pattern of activity in the prefrontal neurons than what appeared when they were correct.

Jamie Roitman, a research assistant professor at the University of Illinois at Chicago, says the new study clears up an unanswered question in numerical cognition: whether there are two steps in naming a numerical value. Previously, it was believed that the brain first learned to summate a quantity of beads or dots or dogs, etcetera, and that higher quantities would be met with greater activity in neurons. Then, a second set of neurons (in the parietal cortex) would determine the corresponding cardinal value—1, 2, 3, 4 and so on. "[The new study] finds that neurons in [the] prefrontal cortex respond similarly when viewing a stimulus of four dots or the symbol '4,' as if these neurons are able to map the symbol onto the cardinal value," she says. "It suggests that this kind of association between symbols and what they represent may occur in the activity of prefrontal neurons."

Nieder believes the work can be applied to humans. "Humans learn to use symbols as mental tools during childhood; prior to the utilization of signs as symbols, long-term associations between initially meaningless shapes and semantic categories must inevitably be established," he says, noting that animals are capable of making rudimentary associations, as shown in this study. "In animal models, we have a chance to learn about the cellular mechanisms underlying such cognitively demanding tasks." 

Oldest Known Jellyfish Fossils Found

Oldest Known Jellyfish Fossils Found

The oldest known fossils of jellyfish have been found in rocks in Utah that are more than 500 million years old, a new study reports.

The fossils are an unusual discovery because soft-bodied creatures, such as jellyfish, rarely survive in the fossil record, unlike animals with hard shells or bones.

"The fossil record is biased against soft-bodied life forms such as jellyfish, because they leave little behind when they die," said study member Bruce Lieberman of the University of Kansas.

These jellyfish left their lasting imprint because they were deposited in fine sediment, rather than coarse sand. The film that the jellyfish left behind shows a clear picture, or "fossil snapshot," of the animals.

"You can see a distinct bell-shape, tentacles, muscle scars and possibly even the gonads," said study team member Paulyn Cartwright, also of KU.

The rich detail of the fossils allowed the team to compare the cnidarian (the phylum to which jellyfish, coral and sea anemones belong) fossils to modern jellyfish. The comparison confirmed that the fossils were, in fact, jellyfish and pushed the earliest known occurrence of definitive jellyfish back from 300 million to 505 million years ago.

The fossils also offer insights into the rapid species diversification that occurred during the Cambrian radiation, which began around 540 million years ago and when most animal groups start to show up in the fossil record, Lieberman said.

The complexity of these early jellyfish seems to suggest that either the complexity of modern jellyfish developed rapidly about 500 million years ago, or that jellyfish are even older and developed long before that time.

Cambrian fossil jellyfish shows similarity to the modern jellyfish, Periphylla. 

Using Satellites to Pinpoint and Predict Pollution

Using Satellites to Pinpoint and Predict Pollution

The European Space Agency is expanding its satellite data network to better track air pollution on a global scale

	BREATH OF FRESH AIR:  ESA's Tropospheric Emission Monitoring Internet Service (TEMIS) provides data on levels of nitrogen dioxide (NO2) in the atmosphere. NO2 is a known pollutant that has been linked to respiratory illness, climate change and acid rain.

As NASA gets to work on the Constellation Program—the space agency's next not-so-small-step for mankind that hopes to put U.S. astronauts back on the moon by 2020—the European Space Agency (ESA) has set its sights on learning more about our own planet. Toward that end the agency this month, at its Tropospheric Emission Monitoring Internet Service (TEMIS) conference in Italy, touted its ability to provide free atmospheric and environmental data to help nations assess air pollution problems.

ESA's TEMIS delivers data in what the agency calls "near-real time" and also provides long-term forecasts based on tropospheric trace gas concentrations, aerosols and ultraviolet (UV) radiation. TEMIS gathers information from its own satellites and also has agreements with NASA and the Darmstadt, Germany–based European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) to make their data available on its Web site. This data includes info from the Ozone Monitoring Instrument (OMI) on NASA's Aura satellite and the Global Ozone Monitoring Experiment (GOME-2) instrument on the MetOp satellite, which was developed by EUMETSAT and ESA to provide a closer view of the atmosphere from low Earth orbit.

ESA plans to expand TEMIS to monitor the transboundary and hemispheric movement of air pollution. The OMI and GOME-2 instruments are spectrometers, which can pinpoint different trace gases in wavelength ranges, providing a measure of Earth's entire atmosphere in a single day.

"Key users of this data are environmental agencies [that] have to report on things like greenhouse gases," says Claus Zehner, an ESA Earth observation application engineer, noting that the European Union (E.U.) continues to keep tabs on air quality over its member nations. By law, they have to report each year on the status of the air quality in their countries, he adds. The E.U. is now considering changing its European Air Quality monitoring laws to mandate the use of satellite data.

SURF'S UP:  ESA Envisat, an advanced polar-orbiting Earth observation satellite that provides measurements of the atmosphere, ocean, land and ice, here illustrates the complexity of the thermal currents at play in the Southern Mediterranean off the coast of Northern Libya.

Among the most important info ESA has provided is data on levels of nitrogen dioxide (NO₂) in the atmosphere. NO₂, a known pollutant, has been linked to respiratory ills and environmental destroyers such climate change and acid rain. Researchers have identified major NO₂ hot spots and industrial culprits, thanks to ESA data gathered between 1996 and 2006.

ESA data has traditionally been used by environmental protection agencies in European Community countries, but its use is spreading. Researchers at Harvard University, for example, used Aura's OMI data to analyze changes in air quality achieved by limiting traffic in Beijing during a China–Africa summit held there last year. In an attempt to ease travel congestion, Beijing officials reduced traffic flow by 30 percent during the conference, barring some 800,000 of its 2.82-million strong fleet of private vehicles from traveling within city limits.

TEMIS enabled Harvard researchers to obtain accurate, independent measurements of NO₂ in the city air at that time. By comparing the satellite observations with measurements from the ground, along with a global chemical transport model, they learned that the atmospheric models failed to accurately reflect a dramatic 40 percent drop in nitrogen dioxide levels in Beijing's air during the traffic restriction, says Yuxuan Wang, a Harvard lecturer and research assistant specializing in atmospheric chemistry.

"Without the TEMIS data, I would say that it would be impossible to do" the Beijing emissions study, Wang says. Chinese scientists were able to provide some data, she says, but it didn't come close to the details captured by the satellites. Wang and her colleagues continue to use ESA data to study regional NO₂ emission distribution as well as gauge the amount of nitric oxide (NO) plus nitrogen dioxide (collectively known as NO_X) present in the air.

ESA data has also been used to study patterns of gaseous pollutant emissions throughout India and to assess the prevalence of disease related to air pollution in New Zealand.

Zehner says that the agency plans to build and launch at least five "sentinel" satellites to monitor not only trace gases that indicate pollution in the atmosphere, but also the surface temperature of the oceans, the movement of ice and the shifting of land masses. The first three are expected to launch by 2012; the remaining two are tentatively scheduled to be sent into orbit by 2015, he says.

ESA's goal is to provide reliable information that can be used to advocate and establish policies designed to improve the environment, Zehner says, adding, "We are offering the first steps needed for monitoring greenhouse gases and other environmental areas."

When the Eyes Play Tricks on the Ears

When the Eyes Play Tricks on the Ears

The way a primitive auditory structure in the brain processes visual information may explain how we are fooled by thrown voices

	AN AUDIO-VISUAL ILLUSIONIST:  Ventriloquists may take advantage of the simultaneous processing of both auditory and visual cues by a brain structure, called the inferior colliculus, to throw their voice to their dummy.

If you watched football or the final game of the World Series yesterday, you may have noticed the following: When the announcers were speaking on camera, it seemed as though the sound of their voices were coming from their mouths. But when the commentary occurred off-screen as the game action was shown, it was quite apparent the TV speakers were the actual sound source of the endless color-commentary babble.

This processing phenomenon in which a visual cue affects how one perceives an auditory stimulus—ventriloquism is another example—may be explained by new research that pinpointed neurons in a primitive brain area that responds to both visual and auditory information. This area, the inferior colliculus region in the midbrain, less than half an inch in diameter, is a way station for nearly all auditory signals as they travel from the ear to the cortex (the brain's central processing area). 

"It's important if you're going to be integrating visual and auditory information that they be on a level playing field, so both are encoded the same way," says Jennifer Groh, an associate professor at Duke University's Center for Cognitive Neuroscience and a co-author of the new work published in Proceedings of the National Academy of Sciences USA. "It's important for the auditory pathway to know where the eye is pointed."

Groh and her colleagues planted electrodes in the brains of three monkeys, targeting 180 individual neurons (or nerve cells) in the inferior colliculus. The animals were placed in a dark chamber where a light-emitting diode (LED) would switch on in one of several predetermined locations. After the monkeys attended to and fixated on the light for a few fractions of a second, a short clip of white noise would play from speakers in the chamber.

When the researchers examined the time-stamped activity of the individual neurons, they observed that each monkey had a neural response in its inferior colliculus when the LED turned on. In addition, two of the three animals showed activity in the auditory structure as they moved their eyes toward the light. In all, the scientists report that more than 67 percent of the neurons monitored (121 of the 180) showed statistically significant responses to the visual stimulus.

"The implication is that it's possible that perception involves more interaction between the sensory pathways than we expected and, because they are happening in low-level areas, they may be more automatic," Groh says. She adds that some cells responded more quickly to the light, although others had a buildup of activity. She speculates that the quicker acting cells process the information whereas the slower ones may encode a reward response (a secondary function of the inferior colliculus).

Christoph Kayser, a research scientist at the Max Planck Institute for Biological Cybernetics in T¨bingen, Germany, calls the new work "stunning." "Results like these suggest that the brain does not try to keep the information provided by the different sensory organs as isolated as possible, but rather that an early mixing of sensory information seems to be the rule," he says. "All this can best be interpreted when seeing the brain as being faced with a flood of sensory information that must be co-registered and merged into a coherent percept." 

Cold spot could be relic of Big Bang

Cold spot could be relic of Big Bang

A cold spot in the oldest radiation in the universe could be the first sign of a cosmic glitch that might have originated shortly after the Big Bang, British and Spanish scientists said on Thursday.

They think this spot -- detected on satellite maps of microwave radiation -- might be a cosmic defect or texture, a holdover from the universe's infancy. But they said their theory would need confirmation.

Such defects or textures, they theorize, reflect a flaw in the pattern of the universe as it formed -- think of a snag in pantyhose or a flaw in a diamond.

"If the cold spot is indeed proven to be a texture, it will completely change our view of how the universe evolved following the Big Bang," said Mike Hobson, of the Astrophysics Group at the University of Cambridge's Cavendish Laboratory, whose study appears in the journal Science.

Hobson, Neil Turok and colleagues at the Institute of Physics at Cantabria based this theory on an analysis of a large cold spot in the cosmic microwave background radiation, which is basically the heat glow left over from the formation of the universe.

The cold spot was discovered in 2003 by NASA's Wilkinson Microwave Anisotropy Probe satellite, and its presence has been the subject of many theories, said Al Kogut of the NASA Goddard Space Flight Center.

Kogut, who did not work on the paper, said if this texture theory is proven, it would offer a window into the universe shortly after the Big Bang some 14 billion years ago, showing places where the universe was expanding and cooling.

"If you imagine water cooling down in an ice cube tray, it will make a transition from a liquid state to solid crystal," Kogut said in a telephone interview.

If that occurs very slowly, he said, that transition goes very smoothly, producing crystal clear ice. But if it goes very fast, the crystal aligns in different directions. Where they don't agree, a crack appears, he said.

This paper "is basically saying this cold spot is a relic of igh-energy physics that occurred immediately after the Big Bang," Kogut said.

"They're claiming they've found one of these things and it could be the tip of the iceberg," he said.

But Kogut, like the study's authors, said he would like more proof. "The evidence is encouraging, but far from compelling," he said.

An undated image of the infant universe with 'warmer' spots represented by red and 'cooler'...