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| March 23,2006 – SOSI Abstract Number: 6 How The Brain Perceived Odor Mixtures; When One Plus One Equals Three, C.B. Warren, PhD, Scientific Affairs Director, Sense of Smell Institute All perfumers know how to make a carnation scent, eugenol (clove) and phenylethyl alcohol (rose) mixed in the right proportions is perceived as carnation, a very different ingredient from either of the starting ingredients. Zhihua Zou and Linda Buck explain what is going on in the brain that gives this effect in the March 10th issue of Science. A very readable summary of this paper can be found on the Howard Hughes Medical Institute's website. Odorants that enter the nose are detected by odor receptors on olfactory sensory neurons which line the nasal cavity. The sensory neurons transmit signals to the oflactory bulb, which then relays these signals to the higher brain area, the oflactory cortex. In both the nose and the olfactory bulb, each neuron appears to be dedicated to only one type of odorant receptor. The situation is different in the olfactory cortex. Zou and Buck found that each cortical neuron received signals from multiople receptors. They reasoned that if this were the case, a combination of two odorants might stimulate both more and different cortical neurons than the sum of the neruons stimulated by each of the odorants alone. This indeed was the case; two odorants, for example, rose and clove, stimulated more and different neurons than the single odorants. In this way a combination of odorants gives rise to a different olfactory picture than can be predicted fromt he odors of the odorants alone. All perfumers know this and spend their careers creating those very special accords which end up being their signature. This does not say that science will put the perfumers out of business, quite to the contrary, the creation of fine fragrance is still very much an empirical art. However, we now have a better feel of why one plus one equals three when it comes to odor mixtures. Zou Z., Buck LB, Science, 2006 March 10;311(5766):1477-81. |
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