Odours can be rated on a scale of pleasantness, which turns out to be an organizing principle for the way humans experience smell, says a new study.
According to the research conducted at the Weizmenn Institute of Science, researchers could tell by measuring the nerve responses whether a subject found a smell pleasant or unpleasant.
In the experiment headed by Prof. Noam Sobel, the researchers inserted electrodes into the nasal passages of volunteers and measured the nerves' responses to different smells in various sites with each measurement capturing the response of thousands of smell receptors.
They found that the strength of the nerve signal varied from place to place on the membrane and it appeared that the receptors are not evenly distributed, but rather are grouped into distinct sites, each engaging most strongly with a particular type of scent.
Further investigation showed that the intensity of a reaction was linked to the odour's place on the pleasantness scale as the site where the nerves reacted strongly to a certain agreeable scent also showed strong reactions to other pleasing smells and vice versa.
"We uncovered a clear correlation between the pattern of nerve reaction to various smells and the pleasantness of those smells. As in sight and hearing, the receptors for our sense of smell are spatially organized in a way that reflects the nature of the sensory experience," Prof. Sobel said.
The implication of the study is that a pleasantness scale is, indeed, an organizing principle for our smell organ.
The study has been published in Nature Neuroscience.