Olfactory Kinematics

I just attended Vivek Jayaraman's Ph.D. thesis defense at Caltech. It's always interesting to attend the thesis defenses from Gilles Laurent's students and track progress through the years. Vivek's talk consisted of three parts. In the first, he presented work from his first Neuron paper, which confirmed and expanded my thesis' findings on invariance to odorant concentration: there are similarities between PNs and KCs responses to different concentrations of the same odorant, putatively allowing odor recognition across concentrations, and yet there are differences between the representations of different concentrations, too --putatively allowing for the coding of concentration. In the third part, he discussed early tests of a new imaging technique.

In the second part, the one that caught my attention, Vivek described experiments with Bede Broome in which they presented pairs of odorants that were overlapping or in close temporal succession. He showed examples of masking (where the presence of the first odor prevents the formation of the representation of the second) and examples where the representation in locust antennal lobe projection neurons (PNs) shifted mid-stream from the representation of the first odor to the late part of the representation of the second.

In this context, Vivek described what he called 'phantom odors': neurons which respond during the transition between presentation of one odorant and another. Furthermore, at least some Kenyon cell responses in the locust appeared to depend on the order in which the two successive odorants were presented. The word 'phantom' has been used in neuroscience before to describe the sensation or percept of a limb that no longer exists. It seems to me that what Vivek described is not (the neural basis of) a percept of an odor that's not there, but rather a representation of a sequence of odors (or of a transition between odors, which may well be an odor in its own right). Might a more fitting name for these Kenyon cells be olfactory dynamics neurons, or olfactory movie neurons?

The study of olfaction has long concentrated on static odor pulses, but the olfactory world is much richer than that. Might this signal the beginning of the mainstream study of olfactory kinematics at last?

Up to Science.