A common theme in mammalian sensory systems is the integration of information from bilateral sensory organs. In vision, binocular comparisons allow for depth perception. In audition, inter-aural cues sub-serve the localization of sound sources. Similarly, the possibility has been suggested that mammals are able to integrate information from the two nostrils to obtain added spatial and non-spatial information about the sensory environment. This work represents a systematic investigation of the contribution of the dual nostril configuration to human olfaction, in both spatial and non-spatial abilities.
In Chapters 2 and 3 the role of the dual nostril configuration in extracting spatial information from smell is studied, from a simplistic left versus right behavioral task carried out in a functional magnetic resonance imager (fMRI), to a complex naturalistic tracking experiment conducted in an outdoor arena. In Chapter 2, we show that humans are capable of performing an odor lateralization task (correctly identifying odor reaching their left or right nostril) in a paradigm using a compartmentalized nasal mask. Previous studies have come to differing conclusions on the human ability to lateralize pure odorants. Our results suggest that this ability is indeed present. In addition the results of the fMRI study that accompanied this lateralization task indicated primary olfactory cortex (POC) as a candidate region for spatial olfactory calculations. We found dissociable responses in POC to odorants delivered to either the left or right side of the nose, a result which implies that information from each nostril is maintained distinctly at this processing level, and could conceivably be used for a comparative left versus right choice. Additionally, in an exploratory whole brain analysis, we identified three bilateral regions of interest (ROIs) that responded preferentially to trials in which subjects were asked to either identify or lateralize the odorants presented. This suggests that separate higher order processing networks subserve spatial abilities in olfaction.
In Chapter 3 we show that human spatial abilities in olfaction extend to a much more demanding naturalistic scent tracking paradigm. We found that roughly two thirds of naive subjects are able to follow a 10m scent trail within one of three attempts, and that humans are capable of vastly improving their scent tracking speed and accuracy with just a few days of practice. In agreement with the results presented in Chapter 2, we found that humans were able to reap an added benefit (in success rate and speed) from using two nostrils to scent track.
In Chapter 4 we set out to ask whether the dual nostril configuration conveys an added benefit for detection of odorants with different chemical sorption rates across the olfactory mucosa. While previous work has suggested that airflow tunes each nostril in a manner that biases olfactory judgments, our results did not show a marked difference in detection threshold to an odorant based on which nostril was used.
|School:||University of California, Berkeley|
|School Location:||United States -- California|
|Source:||DAI-B 68/08, Dissertation Abstracts International|
|Keywords:||Nostril configuration, Olfaction, Primary olfactory cortex|
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