Thursday, December 21, 2023

Coding for Information Overflow and Statistical Irregularity

Part of the "odor code" our brain uses to smell is tasked with overcoming the statistical irregularity caused by massive changes in airflow direction, speed, humidity, etc. as we pull that air through our nostrils. The cross-cancelling variables required in this effort are mentally exhausting to consider, never mind to calculate. But that's what we do when we smell:

How insects track odors by navigating microscale winds
May 2023,

"This is important because insects are typically tracking odor plumes in lower wind speeds, which indicates they are somehow making sense of the high directional variability they encounter," said Houle. "Turbulence intensity is strongly correlated with standard deviations in wind direction, which might be useful for future wind tunnel experimental designs aimed at recreating more 'natural' winds."

Based on their findings, Houle and van Breugel hypothesize an optimal range of wind speed and environmental surface complexity may exist to help insects locate an odor source.

via University of Nevada at Reno: Discovered near-surface wind direction is often highly variable over timescales of less than 10 minutes. They also found wind direction variability to be consistently higher in environments with greater surface complexity (urban areas) and lower at higher wind speeds.

Domestic cats' noses may function like highly efficient gas chromatographs
Jun 2023,

Yet another example of how in olfaction nature is still ahead of technology:

Researchers created a 3D computer model of the cat nose and simulated how an inhalation of air containing common cat food odors would flow through the coiled structures. They found that the air separates into two flow streams, where one spreads slowly above the roof of the mouth on its way to the lungs, and a separate stream containing odorant moves rapidly through a central passage directly to the olfactory region toward the back of the nasal cavity.

In essence, the researchers suggest, the cat nose functions as a highly efficient and dual-purposed gas chromatograph.

via Ohio State University: Wu Z, Jiang J, Lischka FW, McGrane SJ, Porat-Mesenco Y, Zhao K. Domestic cat nose functions as a highly efficient coiled parallel gas chromatograph, PLoS Computational Biology (2023). DOI: 10.1371/journal.pcbi.1011

Each nostril has a unique sense of smell, intracranial electroencephalogram study finds
Nov 2023,

10 subjects with intracranial depth electrodes were delivered an odor to the left, right, or both nostrils through an olfactometer device designed to deliver odors by computer control. Subjects had to identify the odor and indicate which nostril the odor came from. Subjects performed better in detecting and identifying odors in the bi-nostril condition compared to uni-nostril conditions.

Odor identity could be decoded from oscillations in the piriform cortex brain region via neural activity recorded from an intracranial electroencephalogram. The researchers observed that odor identity was encoded in two distinct, temporally segregated epochs in the bi-nostril condition, suggesting a separate smell interpretation occurs via each nostril, suggesting a possible computational advantage in processing odors in stereo. 

via University of Pennsylvania and the Barrow Neurological Institute of Phoenix: Gülce Nazlı Dikeçligil et al, Odor representations from the two nostrils are temporally segregated in human piriform cortex, Current Biology (2023). DOI: 10.1016/j.cub.2023.10.021

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