Monday, February 6, 2006

Rats Smell in Stereo, Study Says

When a rat encounters a savory piece of cheese, it apparently experiences something like what humans do at a fine symphony concert.

New research last week shows that rats smell in stereo, much in the way humans hear. Scientists said rats can precisely detect the location of odors by comparing the intensity and the timing of smells arriving in each of their nostrils. The nasal passages in rats are almost completely isolated from each other and send separate signals to the rodents' brains.

"For a rat, each sniff is a perceptually complete snapshot of the olfactory world," noted researchers Raghav Rajan, James P. Clement and Upinder S. Bhalla of the University of Agricultural Science in Bangalore, India.

The researchers, who published their findings in the Feb. 3 issue of Science, conducted experiments that showed rats learned they could get a drink from a water spout on the left or on the right depending on whether researchers provided them with odor trails on one side or the other. When there was no smell, the rats were not able to pick the right spout based on sounds.

To eliminate the possibility that the rats were detecting airflow patterns through their whiskers, rather than odors, the scientists gave the rats a whisker-cut -- with no discernible difference in performance. Subsequent experiments also showed that when rats were allowed to smell through only one nostril -- eliminating the stereo effect -- their ability to determine the direction of the odors fell sharply.

-- Shankar Vedantam

Huge Masses of Fish Tracked

Researchers at the Massachusetts Institute of Technology have discovered a new way to scout the ocean's depths that might be used to assess the size of fish populations.

The new sonar-based system developed by mechanical engineering professor Nicholas C. Makris, along with colleagues at MIT, Northeastern University and the Naval Research Laboratory, makes it possible to track gigantic fish populations, or shoals, over more than 3,800 square miles. Conventional technology allows researchers to survey just 120 square yards at a time.

The old technique relied on survey vessels sending high-frequency sonar beams into the ocean, but the beams quickly lose strength, like a quickly fading flashlight beam in a dark room. The new technology uses low-frequency sonar that can travel much farther yet still return useful information with the less-intense signals.

With the technology, researchers were able to see large masses of fish for the first time, and found, among other things, that they often assemble in an hourglass pattern, with a relatively small number forming a thin "bridge" connecting the two lobes.

The researchers published their findings in the Feb. 3 issue of the journal Science. Makris said he hopes government officials will use the innovative technology to determine whether certain fish populations are rapidly declining.

"We're able to see for the first time what a large group of fish looks like," Makris said. The older technology, he said, "would be like watching 'Casablanca' and you're seeing one pixel moving across the screen, and that's all you get. You can't figure out what's going on; it's way too slow."

-- Juliet Eilperin

African Slaves' Remains Dated

What may be the oldest remains of African slaves ever found in the Western Hemisphere have been unearthed in the colonial Mexican city of Campeche and dated to the period between the late 1500s and the mid-1600s.

The remains, identified as of African origin through telltale chemicals from the enamel of their teeth, appear to confirm early written histories that described African slaves accompanying explorers and colonists to the New World in the period not long after Christopher Columbus first arrived.

The new study, published in the American Journal of Physical Anthropology, was based on the analysis of teeth from four individuals found in a large multiethnic burial ground near the ruins of a colonial church in an old port city on the Yucatan Peninsula. Archaeological evidence and ancient maps suggest that the graveyard was in use from about 1550 to the late 1600s. The site was uncovered in 2000 by construction workers.

The discovery means that "slaves were brought here almost as soon as Europeans arrived," said T. Douglas Price of the University of Wisconsin at Madison, lead author of the paper. He speculated that the slaves may have been used as domestic servants.

Price and other researchers began studying the site because of distinctive chipping on the teeth, a decorative practice common in Africa. The work was part of a larger effort to study the movement of peoples around ancient Mesoamerica using chemical analysis of teeth. That is done through the study of isotopes of the element strontium, which enters the body through food and is found in all teeth. The strontium isotopes can be identified as coming from particular parts of the world.

-- Marc Kaufman

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