Musée du Parfum & Synesthesia

This afternoon we went to the museum of perfume near the Paris opera house off Metro 8.  The museum is opened by a perfumery called Fragonard Parfumeur.  Fragonard Parfumeur was established shortly after WWI by an entrepreneur named Eugene Fuchs in 1926.  During the tour, we learned about different concentrations of perfume, their making techniques as well as the correct way to put perfume on yourself.  For example, Eau de Toilette is around 10% aromatic compound while the actual perfume is 20%.  Towards the end of the tour, we were given strips of paper scented with different perfumes.  One particular perfume named “Juste un baiser” or “Just a kiss” smelled sweet.  The perfume almost smelled like strawberry and mandarin orange dipped in honey.

Map of the Museum of Perfume

It is interesting how people often use adjectives for taste, or even food items to describe a smell.  We don’t hear people say this flower smells red, or this perfume smells loud.  This must indicate that there are some sort of overlap of brain processing for taste and smell.  This phenomenon is called “synesthesia” in which the stimulation of a sensory pathway leads to involuntary activation of a separate sensory pathway.  There are many different types of synesthesia that are not common to the majority of us.  For example, people with color-graphemic synesthesia view letters and numbers with a specific color (Rich and Mattingley, 2002), and people with number-form synesthesia view numbers in a specific location in space (Sagiv et al., 2006).  Therefore, odor-induced taste might be a universal form of synesthesia that most of us have experienced.

Different types of perfume

If odor-induced tastes are so similar to taste itself that people describe an odor “sweet”, then these odors are probably processed in the same area of the brain as tastes.  Not surprisingly, there are already multiple papers suggesting that the insula, part of the primary gustatory cortex that is responsible for the initial processing of gustatory signals, is also activated by odors that are able to induce taste-like sensations (Stevenson and Miller, 2013).  Instead of looking at the primary taste cortex, Stevenson and Miller (2013) investigated the two secondary gustatory processing areas of the brain: the orbitofrontal cortex (OFC) and the amygdala to see whether odors that induces tastes-like sensation are also processed through similar areas of the brain.  To test their hypothesis, they put 9 patients with brain resections in the anteromedial temporal lobe (AMTL) that included the amygdala, 3 patients with OFC damage, and 42 healthy controls through a series of gustatory and olfactory tests.  All test subjects were presented with 2 sweet-smelling odors (chocolate and plum) and 2 non-sweet-smelling odors (Vegemite and oregano).  An “odor-taste quality score” was based on the test subjects’ ratings of whether a smell is sweet, sour, salty, or bitter compared to the expected taste of the odor (Stevenson and Miller, 2013).  The result of this study shows that AMTL patients, while impaired in gustatory senses, were unimpaired in odor-induced taste tests.  On the other hand, one of the three OFC patients who was severely impaired in gustatory senses, was also impaired in odor-induced taste tests.  The data indicates that one of the two secondary gustatory processing areas, the OFC, is involved in both the processing of tastes, and odor-induced tastes.  Stevenson and Miller (2013) further showed that OFC and insula both have the same type of cells that are more responsible for the discrimination of tastes while the amygdala has cells that supports the recognition of tastes.  This is probably why both the insula and the OFC are needed for the processing of odor-induced tastes while the amygdala is not.

Red part shows the amygdala.

Green part shows the Orbitofrontal cortex (OFC)

This study shows that odor-induced taste is a type of synesthesia that is experienced by the majority of us, which also explains why we often use gustatory adjectives to describe a smell.  However, I think further research is needed to prove this concept because of the low sample size and the fact that only 1 out of 3 OFC patients showed correlation between impairment of taste and odor-induced taste.  In addition, there might be other unknown brain-related problems in these patients, which will affect the interpretation of the data.  Furthermore, an fMRI study of the areas of the brain are active during odor-induced taste tests could potentially provide a more accurate indicator for the overlap of brain processing area of taste and odor-induced taste.  Aside from all the potential flaws of the study, at least now we know that there are biological evidences behind all the taste and food-related description of different kinds of perfume!

-Eric Yao

References:

Rich AN, Mattingley JB (2002) Anomalous perception in synaesthesia: a cognitive neuroscience perspective. Nature reviews Neuroscience 3:43-52.

Sagiv N, Simner J, Collins J, Butterworth B, Ward J (2006) What is the relationship between synaesthesia and visuo-spatial number forms? Cognition 101:114-128.

Stevenson RJ, Miller LA (2013) Taste and odour-induced taste perception following unilateral lesions to the anteromedial temporal lobe and the orbitofrontal cortex. Cognitive neuropsychology 30:41-57.