FoundationalConceptsNeuroscience

ious, reminiscent of mothballs and often mentioned as a contributor
to the odor of feces. Indole is indeed present in human feces—where
it occurs as a breakdown product of the amino acid tryptophan, a
component of proteins. And yet it is also part of the alluring aroma
of jasmine, and many other flowers, too. In synergistic combination
with dozens of other molecules, many of which are present in only
very small concentrations, the noxiousness of indole contributes to
the exotic complexity of jasmine’s aroma. Perfume manufacturers
sometimes add synthetic indole to commercial perfumes, attempt-
ing to replicate nature’s symphony, but such attempts invariably fall
short.
A jasmine-like aroma is also present in several other species of
plants unrelated to Jasminum. For example, there is Nicotiana alata,
ajasmine-scented cousin of smoking tobacco, and Chinese wisteria
(Wisteria sinensis), a woody, climbing vine with spectacular hanging
flowers. Many varieties of daffodil (genus Narcissus) also have a jas-
mine quality to their aroma—sniff for it.
Although the aromatic qualities of plants are related to complex
mixtures of many different molecules having a variety of molecular
shapes, often one or two molecules in the mix identify strongly with
the particular odor of the plant. For example, if one were to smell a
pure preparation of the molecule benzyl acetate, one would have no
problem identifying it as a jasmine aroma. A significant part of what
we would call the characteristic aroma of a jasmine flower seems to
be associated with neural pathways activated by benzyl acetate. The
many other molecules present in the essential oil of jasmine impart
nuance and complexity to the plant’s aroma.
Similarly with lemon: the molecule geranial, one of the compo-
nents of the essential oil of lemon, is readily identified with the aroma
of lemon. And with rose, the molecule geraniol, a component of the