It was, perhaps, the most inauspicious start to a TedTalk I’ve ever known. A shiny guy, wandering back and forth, telling the audience that soon they would be experiencing the top notes of a fragrance, Beyond Paradise, which had been split up by the perfumer who created it for Esteé Lauder into “successive bits”. 1 Watching them on the iPod, I don’t often miss not being there for a TedTalk. But this was unfair. I soon forgot that.

Luca Turin addressed one of the neuroscience questions that has always puzzled me: how do we detect smell? Why does one molecule smell like this and another like that?2 The prevailing view, so prevailing that no alternatives exist on an industry website, is that there's a kind of lock-and-key mechanism. The shape of the odorant fits the shape of a receptor and triggers it to fire. The brain interprets the pattern of impulses as a particular smell. I've honestly never felt too comfortable with this. So many molecules, so many smells, so few receptors.

Turin also doesn’t believe the shape theory. He unearthed another theory, that the vibrational frequency of a molecule is what triggers the receptor. And he presented some evidence. Molecules with very similar shapes -- but different “notes”, to deliberately abuse the perfumers’ term -- that smelled very different. And molecules with the same note, but different shapes, that smelled the same. Better yet, he put his money where his mouth is, and started a company to make odorants to order. Turin talked about the search for a substitute for coumarin, which has a manly kind of warm hay tobacco smell and is a carcinogen. They found a molecule with a rather different shape but the same vibrational pattern, and it smelled like ... warm hay tobacco: coumarin.

The big point is that tonkene, as they called it, after the Tonka bean3
that is a primary source of coumarin, is not carcinogenic, and is exactly what the fragrance industry wanted. They frankly couldn’t give a stuff whether it vibrates or is shaped just right. It does what they need it to, and they’re prepared to pay for it.

That, I think, was Turin’s big point. It's interesting to know exactly how the molecules talk to the brain, and he even had a stab at suggesting how vibrational energy triggers a response in the cell, but in the end what really counts is being able to make predictions that are borne out in the real world. The battle between shape and vibration is not over yet, but while the shape guys don’t really have a predictive theory of anything, the vibration guys do, and can use it.

I started off upset that I was missing something in Turin’s TedTalk, and ended up feeling that this was one of the few TedTalks I’ve experienced that wasn’t long enough.

  1. “Beyond Paradise transports you to a perfect world of optimism and wonder. Unfolds on your skin with a fascinating blend of tropical wetness, zesty freshness and bursting floralcy.”  

  2. The other, since you ask, is how on earth synaptic connections “are” memories.  

  3. No, not the toys: Dipteryx odorata.  

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