SPLTRAK Abstract Submission
Evidence for Primacy Coding in Human Olfaction
Terry Acree1, Chloé Albietz2, Dmitry Rinberg3
1Cornell University, Ithaca, NY, United States
2Givaudan, Lausanne, Switzerland
3New York University, New York, NY, United States

Object recognition is one of the basic properties of all sensory systems. Humans and other animals can identify smells independently of their concentrations. Recently, we proposed a novel model for concentration invariant odor recognition, based on the importance of earlier activated receptors. A higher concentration of an odorant activates a larger population of the receptors. Thus, only a small ensemble of receptors, which is activated by both low and high concentrations can be responsible for odor identification. According to our model, called Primacy coding, this ensemble is activated first and defines an odor identity. Recent animal experiments provide an evidence toward this model. Mice can discriminate odors based only on a short temporal window (~100 ms) at the beginning of a sniff cycle (Wilson 2017) and cortical representation is formed very quickly after an onset of odor exposure (Bolding 2017).   Can this model be applied to human odor perception? We designed an experimental approach based on a binary odor mixture discrimination. Subjects were asked to identify odors A or B delivered simultaneously at different concentration ratios. We estimated a concentration ratio correspondent to equal probability of detecting odor A or B: Equal Odd Ratio (EOR). Our apparatus allowed us to controllably change the relative timing of individual odorants delivery with less than 50 ms temporal precision, while keeping all other parameters of odor delivery the same (Rochelle 2017). We found that the delivery of odorants at EOR with a temporal shift, systematically increased probability of detecting an earlier odorant. And this effect is observable at temporal shifts smaller than 50 ms. This is strong evidence that early events during odor exposure are responsible for odor recognition in humans.