Neural Cartography

This first article doesn't sound like the cartography I came here for, but it's in the title so...

Researchers present insight into the neural cartography of smell

Oct 2022, phys.org

https://medicalxpress.com/news/2022-09-insight-neural-cartography.html

Honestly I'm unclear as to what this means; the endoplasmic reticulum has some mediating influence on the neural computations that turn olfactory receptor stimulus into the olfactory perception of a specific odorant?

"It is mind-blowing," said Dr. Lomvardas, also a professor of neuroscience and of biochemistry and molecular biophysics at Columbia's Vagelos College of Physicians and Surgeons. "This system found a way to create a genetically encoded, hard-wired means of transforming randomly-chosen receptor identity to a very precise target in the olfactory bulb."

Perhaps, olfactory neurons are not alone in the way endoplasmic reticulum stress organizes their wiring with downstream neurons. "If it turns out that all neurons do this, this discovery could help us understand much more about the brain," said Shayya.

via Mind, Brain and Behavior Zuckerman Institute at Columbia University:  Hani J. Shayya et al, ER stress transforms random olfactory receptor choice into axon targeting precision, Cell (2022). DOI: 10.1016/j.cell.2022.08.025

https://dx.doi.org/10.1016/j.cell.2022.08.025

Image credit: AI Art - Number Two Number One - 2022

Here's another article that makes reference to "maps" but isn't actually about navigation...

Mapping the path from smell to perception

Nov 2022, phys.org

https://medicalxpress.com/news/2022-10-path-perception.html

"The last frontier of sensory neuroscience"

Because previous studies of the olfactory cortex failed to find any logical organization among neurons there, many neuroscientists suspected information about odors was relayed randomly through the brain. But those studies examined connectivity patterns of just a few dozen neurons.

DNA-based brain-mapping technologies charting the way sensory information is routed between olfactory-processing parts of the brain including the olfactory bulb, which receives sensory information from the nose, the primary smell-processing hub called the piriform cortex, and several other brain regions that receive inputs from the olfactory bulb.

via Cold Spring Harbor Laboratory: Yushu Chen et al, High-throughput sequencing of single neuron projections reveals spatial organization in the olfactory cortex, Cell (2022). DOI: 10.1016/j.cell.2022.09.038

https://dx.doi.org/10.1016/j.cell.2022.09.038

And finally, a little something about how we use olfaction to navigate...

Flies smell the motion of odors and use it to navigate, study finds

Nov 2022, phys.org

https://phys.org/news/2022-11-flies-motion-odors.html

Flies can sense the direction of moving odor packets themselves, not just the wind.

Cool study design: They genetically modified fly antennae to detect light, then created fictive odor packets out of light and watched how the flies responded to these signals in both windless and windy environments.

via QBio Institute at Yale: Nirag Kadakia et al, Odour motion sensing enhances navigation of complex plumes, Nature (2022). DOI: 10.1038/s41586-022-05423-4

https://dx.doi.org/10.1038/s41586-022-05423-4

On Olfactory Navigation

I purposely read this book Supernavigators (2019) hoping to get some snippets on using our sense of smell to find things, and I wasn't disappointed. 

Humans were led to a random location within a room diffused with two odors. After brief sampling and spatial disorientation, they had to return to this location. Humans located the target with higher accuracy in the olfaction-only condition than in the control condition and showed higher accuracy than chance. 

-Jacobs, L.F.; Arter, J.; Cook, A.; and Sulloway, FJ. (2015). "Olfactory orientation and navigation in humans," PLOS 'One, 10(6), e0129387. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4470656/

Note there are two different versions of olfactory navigation -- one where you track an odor to its source (this relies heavily on bilateral input, aka stereo-olfaction) and the other, much more common for modern-day humans, is when you identify a place by its odor. We usually have our eyes open, and being the ocularcentric creatures that we are, we are likely to use visual cues and not even realize the odor-identity of a place. 

But it doesn't stop here, the rabbit hole continues, and this one goes all the way back to the golden days of behavioral science, when rats told us everything we wanted to know about ourselves: 

This report is ultimately based on rat experiments, with the "men" part being only conjecture by the researcher; and he concedes, "My argument will be brief, cavalier, and dogmatic. For I am not myself a clinician or a social psychologist. What I am going to say must be considered, therefore, simply as in the nature of a rat psychologist's ratiocinations offered free.

*Ratiocinations are another word for thoughts that also happens to remind the reader that we're talking about rats (he italicized the rat in ratiocinations).

The "mapmaking" happens during what they call "Vicarious Trial and Error" or "VTE'" and described as "the hesitating, looking-back-and-forth, sort of behavior which rats can often be observed to indulge in at a choice-point before actually going one way or the other." If you're not a scientist, you can probably just call it "thinking."

via Berkeley Labs: Tolman, E.C. (1948). "Cognitive maps in rats and men," Psychological Review, 55(4), p.189.

https://web.csulb.edu/~cwallis/382/readings/482/tolman.%20cognitive_maps_in_rats_and_men.1948.html

Image taken from the Silver Bible of Interior Design Standards

And with that, let us not forget that olfaction is the first sense. Before all the other ways we sense our environment, bacteria and fungi were using chemotaxis, detecting and navigating their way through a world of chemical gradients. The essay at the end of Hidden Scents, called "Olfactory Space and n-Dimensionality" tells the story of the primordial eukaryote as it chemo-taxis its way through evolution, past the multi-cellular organism, the chordata (animals with vertebrate), and eventually to the big-brained, smooth-skinned monkeys that we are today.

The neocortex is an outgrowth of the nose-brain, and not the other way around, and therefore olfaction can be a useful model for understanding the n-dimensional information network in which our brains operate. The world is typically understood as a 3-dimensional space, but in fact, from the perspective of the brain, we are navigating and interacting with an infinitely-dimensional information space. 

 

Categorgonzola

A perennial topic on this weblog is the categorization of smells. Today I'm looking at a study from 2011 that looks at common features that group smells together. One of the common denominators is hedonics, or pleasantness vs non-pleasantness.

It always makes me pause to think about this, because it seems that people can never really agree on what makes a smell good or bad, and yet the hedonic dimension is the only one that keeps coming back as the primary distinction between odors. I guess that's just the law of large numbers at work, a law which is against natural human cognition.

If you include enough people in your study, the differences between us cancel out and you're left with a fuzzy but recognizable picture of a smell map, which is seen above.

The other common denominator (it’s not a denominator if there’s two, right?) is a dimension the researchers call natural/chemical.

This map is organized as follows: Whereas the pleasantness of an odor can be predicted on the number of carbon atoms per molecule (related to how fast it evaporates), the natural/chemical dimension is predicted by the polarity of the molecules, or how attracted they are to water.

Why? Not so sure. Mention is made to the difference in the olfactory receptors themselves - some are from when we were fish and some are from when we became land animals, so the two may have a different relationship with water (polarity).

For example, odorants are dispersed more slowly in the water. Also, smellable molecules to fish don’t have to be volatile organic compounds, because for a fish, the air itself is already a liquid. So fish detect water soluble molecules whereas humans detect airborne molecules.

Actually, now that I look at the ‘natural’ part of the map, I realize that none of those things exist underwater, right? Burnt? Nope. Moldy? Although mold is always associated with moisture, it doesn’t grow underwater. And Earthy? Kind of the opposite of water.

Natural - Burnt, Smoky, Nutty, Woody, Resinous, Musty, Earthy, Moldy, Almond, Popcorn, Peanut Butter, Oily, Fatty, Warm, Dry, Powdery

Chemical - Etherish, Anaesthetic, Chemical, Medicinal, Disinfectant, Carbolic, Sharp, Pungent, Acid, Gasoline, Solvent, Cook, Cooling, Cleaning Fluid, Paint, Camphor

Good - Fragrant, Sweet, Perfumery, Floral, Light, Aromatic, Cool, Cooling, Fruity, Citrus, Rose

Bad - Sharp, Pungent, Acid, Heavy, Musty, Earthy, Moldy, Burnt, Smoky, Oily, Fatty, Sour, Vinegar

-image source: link

Notes:

In search of the structure of human olfactory space. A. A. Koulakov, B. E. Kolterman, A. G. Enikolopov, D. Rinberg. Front. Syst. Neurosci. 5, 65 (2011).

doi: 10.3389/fnsys.2011.00065

On Space and Place

Confused John Travolta

The hypothalamus is called the seat of social behavior. The hippocampus is the thing that knows where you are, your internal GPS. Together, these brain parts, along with your olfactory system, of course, influence all of your decisions. Everything we do is dependent on where we are (or where we think we are) and who we’re with (or who we think…). Olfactory data informs these things. Places and the smell of those places are centrally located both in the memory and in the motivating, motility actuating parts of us. The emotions that drive us are informed by the smells of the places we are in.

This new report shows that there may be very specific cells that can tell who’s house you’re in. (The experiment is on male mice and other male’s habitats.) They’re looking to use this to help people with social disorders, like autism, schizophrenia, depression, and social anxiety. Anyway, this just points to the use of olfactory studies to help with larger social problems.

Smell tells intruder mice how to behave

phys.org, Jun 2016