Neuroscience For Kids

Human Olfaction: Nothing to Sniff At!
December 21, 2006

The human sense of smell has often been considered to be one of the weaker senses. New experiments using college students as subjects reveal that our sense of smell may be better than we think. Researchers at the University of California, Berkeley, have found that humans:

1. Can follow scent trails ("scent-track")
2. With practice, improve their ability to scent-track
3. Sample different portions of the air with each nostril
4. Are better at scent-tracking when they use BOTH nostrils

In the first of five experiments, the scientists had 32 subjects wear masks to block sight, earmuffs to reduce sound and thick kneepads, elbow pads and work gloves to reduce touch sensations. These subjects then got down on their hands and knees and tried to follow a 10-meter-long scent trail placed on a grass field. Of the 32 subjects, 21 were able to follow the scent trail to its end.

With additional training (three times per day, three days in a two-week period), the subjects improved their scent tracking ability. After training, subjects took a straighter line and were faster at following the scent trail.

Each nostril appears to receive air from distinct areas of space. Imaging of the air trail into each nostril showed that the nostrils sample air separated by about 3.5 cm. To test if two nostrils were better than one, the researchers tested scent-tracking ability again: once when one of the subject's nostrils was taped closed, and again when the subject used both nostrils. Subjects were LESS accurate and slower in scent-tracking when only one nostril was used. The scientists repeated this experiment with a device that could stream the same air into both nostrils. Again, subjects were less accurate and slower when each nostrils received similar information.

Although our sense of smell may be better than once thought, it still doesn't come close to that of dogs. Some dogs can follow scent trails that are two days old!

References and more information:

1. Porter, J., Craven, B., Khan, R.M., Chang, S-J., Kang, I., Judkewicz, B., Volpe, J., Settles, G. and Sobel, N., Mechanisms of scent-tracking in humans, Nature Neuroscience, 10:27-29, 2007.
2. Bloodhounds: King of the Trackers - Neuroscience for Kids
3. The Nose Knows - Neuroscience for Kids
4. Our Chemical Senses: Olfaction - Neuroscience for Kids

Copyright © 1996-2006, Eric H. Chudler, University of Washington