The role of the olfactory recess in olfactory airflow

Abstract

The olfactory recess -a blind pocket at the back of the nasal airway -is thought to play an important role in mammalian olfaction by sequestering air outside of the main airstream, thus giving odorants time to re-circulate. Several studies have shown that species with large olfactory recesses tend to have a well-developed sense of smell. However, no study has investigated how the size of the olfactory recess relates to air circulation near the olfactory epithelium. Here we used a computer model of the nasal cavity from a bat (Carollia perspicillata) to test the hypothesis that a larger olfactory recess improves olfactory airflow. We predicted that during inhalation, models with an enlarged olfactory recess would have slower rates of flow through the olfactory region (i.e. the olfactory recess plus airspace around the olfactory epithelium), while during exhalation these models would have little to no flow through the olfactory recess. To test these predictions, we experimentally modified the size of the olfactory recess while holding the rest of the morphology constant. During inhalation, we found that an enlarged olfactory recess resulted in lower rates of flow in the olfactory region. Upon exhalation, air flowed through the olfactory recess at a lower rate in the model with an enlarged olfactory recess. Taken together, these results indicate that an enlarged olfactory recess improves olfactory airflow during both inhalation and exhalation. These findings add to our growing understanding of how the morphology of the nasal cavity may relate to function in this understudied region of the skull.

How much does nasal cavity morphology matter? Patterns and rates of olfactory airflow in phyllostomid bats

“…We performed a grid-refinement study by examining patterns and rates of flow in models with twice and four times as many bricks. We did not find notable differences in either parameter, corroborating our previous work [4], and indicating that the approximately 625 000-tetrahedra models were sufficient for this study.…”

“…The implication of this finding is that, rather than sequestering recently inhaled air from exhalation, the primary functions of the olfactory recess in these phyllostomid bats may be to expand the surface area available for the olfactory epithelium and slow down inhaled air to improve odorant absorption across this epithelium. Some computational support for this idea was found by Eiting et al [4], who showed in an experimental modelling study that, all else being equal, a larger olfactory recess produces lower rates of flow through this region during exhalation.…”

“…For each species, we constructed a 3D stereolithography (STL) file from the CT scans as follows (see [4] for additional details). First, an image stack was brought into MIMICS v. 16.0 (Materalise, Leuven, Belgium).…”

“…These features include a narrow, dorsal conduit for olfactory airflow, an enlarged cavity (the olfactory recess) at the back of the nasal airway and a clear separation of the olfactory region of the nose from the respiratory region [1][2][3][4]. All of these features impact the way air moves through the nasal cavity.…”

“…Within the ethmoturbinate region is the olfactory recess, which is a blind pocket at the back of the nasal cavity. The principal function of the olfactory recess may be isolating the inhaled, odorant-laden air from exhaled respiratory air currents, which would otherwise be washed out by freshly inhaled odorants from the ethmoturbinate region [4][5][6][7].…”