Sun, Feb 19, 2006 - Page 19 News List

Rats: smelling in stereo

Just one quick sniff is all it takes for a rat to locate the source of an odor


English literature is rife with references to the smelling of rats, as in the classic verse report on maternal care in Felis Silvestris Catus.

"What! washed your mittens, you are good kittens. But I smell a rat close by."

The scientific literature, on the other hand, is more concerned with how rats smell -- that is to say, how they detect and process odors. And the answer, reported in the current issue of the journal Science is -- in stereo.

Rats, as many of us, inside and outside of neuroscience have suspected, use their sense of smell to find the source of odors, good and bad.

They and other animals are much better at this task than humans. Witness the common behavior patterns of juvenile human males, who are so incompetent at pinpointing the location of unpleasant odors that they discuss the problem endlessly.

Rats have no such problem, as Raghav Rajan, James Clement and Upinder Bhalla at the University of Agricultural Science in Bangalore, India, have recently demonstrated.

They trained rats to associate an odor with water. Then the rats had to determine whether the odor was coming from the left or the right. This was done with the kind of contraption that Wizard would have loved.

Two water spouts, of the kind that go in the hamster or rat cage, were mounted on a sheet of Plexiglas with a "sniff port" between them -- a hole in which the rat could poke its nose. The odor was released from either side of the hole and the water was available only from that side.

The thirsty rats (water deprived) had to figure out which spout to lick based on the source of the odor, and they did superbly. They were also fast -- sometimes needing only one quick sniff.

Using brain probes, the researchers found that the sensory infor-mation from each nostril was processed separately in the brain, giving the rats enough data to determine location, even though the nostrils are not very far apart.

This discovery comes on the heels of recent work suggesting that dogs can sniff out very low concentrations of chemicals produced by cancer cells. These are both reminders of the exquisite sensitivity of animals and the limits of the human sense of smell.

These limits may not be such a bad thing. Having a good nose is not always a blessing, as I can testify, because the world is full of good odors and bad and I tend to smell things that other people don't. I recently sat down for lunch at a restaurant and had to leave immediately because the place smelled like there was something dead somewhere on the premises.

But, and here's the amazing part, the restaurant was almost full and none of the diners were making the "what is that awful smell" grimace. They seemed to have been blessed with some sort of selective anosmia.

Would it have helped if I had had a stereoscopic smell with the ability to pinpoint odor sources? I'm not so sure. Then I would have known exactly where the dead thing was, and how would that have helped me? I would be able to determine immediately whose perfume was choking me in an elevator. That couldn't have good results.

On the positive side, I would have figured out faster than I did where in the minivan one of my offspring had sequestered the remains of a roast beef sandwich that eventually threatened to make it undrivable.

It's no accident that Superman had X-ray vision but not the equivalent sense of smell. Otherwise he would have been sent into a coma by the ripe symphony of Gotham.

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