Thursday, July 18, 2019

Who Nose? -- Nothing to Sniff at: Mammalian Brains and Distinguishing Odors


     "Neuroscientists have discovered that at least six types of mammals -- from mice to cats -- distinguish odors in roughly the same way, using circuitry in the brain that's evolutionarily preserved across species.




       The world is filled with millions distinct smells, but how mammals' brains evolved to tell them apart has been something of a mystery.




       Now, in a study published today, two neuroscientists from the Salk Institute and UC -- San Diego have discovered that at least six types of mammals distinguish odors in roughly the same way, using circuitry in the brain that's evolutionarily preserved across species.




      "The study yields insights into organizational principles underpinning brain circuitry for olfaction in mammals that may be applied to other parts of the brain and other species," says Dr. Charles Stevens, distinguished professor emeritus in the Salk Lab.





     In brief, the study reveals that the size of each of the three components of the neural network for olfaction scales about the same for each species, starting with receptors in the nose that transmit signals to a cluster of neurons in the front of the brain called the olfactory bulb which, in turn, relays the signals to a "higher functioning" region for odor identification called the piriform cortex.




     "These three stages scale with each other, with the relationship of the number of neurons in each stage the same across species," says Dr. Shyam Srinivasan, assistant project scientist with UC San Diego's Kavli Institute for Brain and Mind, and the paper's coauthor. "So, if you told me the number of neurons in the nose, I could predict the number in the piriform cortex or the bulb."




      The current study extends research by the same authors, published last year in which described how mouse brains process and distinguish odors using what's known as "distributed circuits." Unlike the visual system, for example, where information is transmitted in an orderly manner to specific parts of the visual cortex, the researchers discovered that the olfactory system in mice relies on a combination of connections distributed across the piriform cortex.




     Following that paper, the authors sought to determine if the distributed neural circuitry revealed in mice is similar in other mammals. For the current work, the researchers analyzed mammal brains of varying sizes and types. Their calculations, plus previous studies over the past few years, were used to estimate brain volumes. 



      The new study revealed that the average number of synapses connecting each functional unit of the olfactory bulb to neurons in the piriform cortex is invariant across species.

      "It was remarkable to see how these were conserved," says Dr. Stevens.



     Specifically, identification of individual odors is linked to the strength and combination of firing neurons in the circuit that can be likened to music from a piano whose notes spring from the depression of multiple keys to create chords, or the arrangement of letters that form the words on a page.



       "The discrimination of odors is based on the firing rate, the electric pulse that travels down the neuron's axon," says Srinivasan. "One odor, say for coffee, may elicit a slow response in a neuron while the same neuron may respond to chocolate at a faster rate."



      This code used for olfaction is different than other parts of the brain.

     "We showed that the connectivity parameters and the relationship between different stages of the olfactory circuit are conserved across mammals, suggesting that evolution has used the same design for the circuit across species, but just changed the size to fit the animals' environmental niche," says Dr. Stevens.



     In the future, Dr. Stevens plans to examine other regions of the brain in search of other distributed circuits whose function is based on similar coding found in this study.



     Dr. Srinivasan says he will focus on how noise or variability in odor coding determines the balance between discrimination and learning, explaining that the variability the duo is finding in their work might be a mechanism for distinguishing odors, which could be applied to making better machine learning or AI systems."




     Smell-o-vision, anyone?

Stay cool and not stinky,
Steph

63 comments:

  1. While the pictures of animals sniffing flowers are so cute (that I want to wretch), I wonder if that's an anthropomorphic view? I've never seen a cat sniff flowers, and the only time I've seen that in ungulates is in anticipation of consumption.

    Less cynically and more scientifically, I wonder whether the "combination of connections distributed across the piriform cortex." may explain why certain smells become rooted deep into our subconscious, especially smells from early childhood. And in a similar vein how much smell is used for identification between parents and youngsters; I think I've heard this is the case for sea lions and similar creatures that leave the young while fetching food. They all look the same to me.

    Maybe I'll read the study instead of turning up my nose.

    FYI Smith has a prominent place in this month's Harper's Crossword, which was significantly harder than usual.

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    1. My dog stops to smell flowers. Now, perhaps they have had dog urine on them, too...Sorry about the cuteness overload.

      Yes, I had the same thoughts about smells being so deeply rooted because the connections are widely distributed across the piriform cortex.

      Thanks for the heads up on the Smith clue.

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    2. Makes me wonder about the psychological levels in other species. We know play is found in mammals - including adults, for example wolverines that slide down snow hills. What is the sense of aesthetics in animals, in particular that go beyond function (like Bowerbirds, that build to attract mates)?

      Elephants seem to honor their dead, almost a religion. Cats are drawn to catnip, dogs are drawn to all sorts of disgusting things, can animals appreciate smells for their own sake?

      Must be Friday.

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    3. I have watched Maizie watch sunsets, taking it all in. Why not smells?

      Of course Gary Larson is spot on, as always.

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    4. Here's an article that will get your goat (it links to the original study with all sorts of science-y stuff.

      "Researchers involved in the study had previously concluded that goats can express emotion through their voices. Next, a larger team decided to explore whether goats can detect it in others."

      Would it make sense to be able to express emotion if others couldn't detect it? What would be the point of calling into the wind? And I suspect this will come as no surprise to anyone with mammal pets. I suspect Maizie can sense your mood.

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    5. eco, thanks for the goat article. I have so many more questions!

      Yes, I imagine Maizie senses my awe, especially around wildlife, sand dunes, sunrises and sunsets.

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  2. I can't see what's pear-shaped about the piriform cortex. Interesting that this small structure includes the Area Tempestas, which is involved in triggering epileptic seizures. This led me to read more and confirm that specific odors can trigger seizures, and vice versa.

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    1. jan, odors triggering seizures makes sense. We hear so much more about flashing lights being the culprit.

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    2. "No sooner had the warm liquid mixed with the crumbs touched my palate than a shudder ran through me..."
      -- Proust, Remembrance of Things Past

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    3. ..."specific odors can trigger seizures, and vice versa." On the vice versa part, are you saying seizures can trigger specific odors? I definitely don't want to think about that.

      But I've long suspected smells might be embedded in the deeper parts of our brains. I wonder if the same is true for sounds, especially music. Where are my Baby Mozart cassettes?!?!?

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    4. Yes. E.g., temporal lobe seizures may result in the patient experiencing a peculiar odor, like burning rubber. I imagine it may be analogous to a migraine aura.

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    5. jan, thanks for the Proust reference. Classy-ing up PEOTS!

      eco, the vice versa part is intriguing, as is your question about sound. Can you play those cassettes on your boom box?

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    6. Burning rubber is DEFINITELY preferable to the odors I was imagining.

      WW: I can play them on my boom box AND on my Walkman, too bad they don't have them on 8 track for my car.

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  3. And related to last posting's slots, have you ever been to the Bisti Badlands?

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    1. The connection to a meteorite strike is tenuous at best.

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    2. I think the context for noting the strike was that this was once a fertile valley with lots of organic material that is now part of the landscape. Plus deadly meteor strikes make good headlines, like my earlier posting.

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  4. I'm packing my bags for GJ 357 d. Just 31 light years away, Elon Musk will have us there in no time.

    It's great we're discovering so many exoplanets, including this one for people from Texas.

    But I still wonder if we're severely undercounting? We can only "see" a planet from solar flicker, and maybe some distortions in the star's movement. The former requires the planet's orbit to transit the line between its star and our observation.

    Given the great distances (nearly infinite for geometric purposes) and assuming the planets are relatively small compared to their sun, a path that is, say, 1° off tilt to our line of sight would be invisible to us. Thus it is very unlikely that a planet's orbit would be visible, roughly 1 chance in 180.

    This assumes the planet has a relatively consistent planar orbital path, as do the planets in our solar system. And I don't think there's reason to believe all the planetary systems would align throughout the galaxy....

    Or is there an astronomer in the house that can clarify/ correct my reasoning/

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    1. I believe the plane of our solar system aligns pretty well with the plane of the Milky Way galaxy, and I'd imagine that most other stellar systems in our galaxy do as well, given the current thinking about the origins of such systems. Obviously, other galaxies don't, else we'd never see another spiral galaxy as such.

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    2. Actually that's not the case. According to this site (my alma mater) our solar orbit is at a +/-63° angle to the galactic disk, which of course is only relatively flat.

      Other websites give different angles (60° to 67°), but it doesn't really matter. As the Cornell site notes the galactic influence is insignificant on a solar system's orbital path.

      So I maintain my theory that we've only seen the tip of the planetburg.

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    3. And I guess it isn't my theory, as this site shows. Their little gif makes it very clear, 1 pic = 1000 words.

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    4. Last thought: a Jupiter-sized planet with Mercury's orbit around a star the size of our sun would only have to be out of our sight line plane by 1/10 of 1° to be outside transit. Changes the odds to 1:1800.

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    5. True, and I did imply such in my initial statement - though I didn't know many of the methods that are more recently in use. Transit is still the main method, and my original point is that there is more we don't know than we do. I look forward to astronomers using these methods to find more exoplanets, they just haven't done that YET.

      The Reflection/ Emission Modulation seems promising, though it is limited in the type (size and distance) of planets it can detect.

      I'm pleased that the article more or less confirms my math: "For a planet orbiting a Sun-sized star at 1 AU, the probability of a random alignment producing a transit is 0.47%." This is 1:212, not too far off from my initial 1:180. I now need medical attention for spraining my shoulder by patting myself on the back.

      The graphic representation I did (and confirmed to myself, at least) that put this at around 1/10 of that was incorrect didn't have the correct sun size (a scaling problem, in theory I could draw full size but I don't want to abuse Autocad). As I revisit it looks like the maximum orbital plane or a sun-sized star is a bit less than 1 degree out of 180.

      Some math: sin 0.85° = 0.0148 * 29,0000,000 miles (Mercury's perihilion) = 430,207 miles. Our star's diameter is about 864,000 miles, so if a planet's orbit were just a bit more than 0.85° "off-tilt" we would not see it. Our own distance relative to this has some effect, but it's so large the sin of that is effectively 0.

      But I don't study this seriously, and am going back to bed.

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    6. and that should be "...the maximum orbital plane for a sun-sized star..."

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  5. Replies
    1. eco, I told Maizie about the Big Bird. She was nonplussed.

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    2. If such a bird were around I think Maizie would be minused.

      Although mega fauna have a pattern of disappearing when humans show up.

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    3. You say minused; she says nonplussed.

      Sadly, true re: humans.

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    4. Maizie is smarter than me.

      There used to be a guy who hung out in Fisherman's Wharf dressed in a pirate outfit with his faithful parrot. He called himself a street performer; we called him sh*t shoulders.

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  6. They call these vacation spots, but I don't see a single cotton candy stand.

    Perhaps Jan has been to the "Ether Dome"? A disappointing moniker, I was hoping for a wilder trip. I confess I've only seen 2 of these sites, and you?

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    1. Two for me as well--Earthquake Trail and Fly Geyser.

      Have you been to "ether" one?

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    2. I haven't been to any of the sites, though we walked past MGH's Museum of Medical History and Innovation less than 4 hours ago, getting our granddaughter to school. We've talked of stopping in some time; now I'll have to.

      Don't think I've ever been to BNL, though I have been to the Brookhaven airport nearby.

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    3. I've been to the Earthquake Trail and seen the Delmarvalous birds, though before bald eagles were in abundance.

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    4. I wrote a paper on the evolution of the medical theater for an architectural history class. I focused on Davidge Hall at the University of Maryland (Baltimore campus) which is the oldest still in use.

      They had an extensive spittoon drainage system in the Hall, but that's been removed. When I was there they had some artifacts in cases, but not a real formal museum. I made the unfortunate mistake of wandering down a lonely hall, pulling back a sheet to uncover Hermie, the school's mascot. Early 20th Century photos of students posing with Hermie (dressed like Santa) added to the fun.

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    5. The College Park campus of the University of Maryland is adjacent to the oldest continuously operating airport still in use. Back in the days when I owned half an airplane and the World Wide Web hadn't been invented, I needed to visit the Patent Office. I was too inexperienced at that point to want to fly into National Airport (which I later enjoyed doing), so I flew into College Park. The Metro at that point didn't extend out that far, so I caught a cab for the nearest Metro station (I forget which). Coming back later in the day, I asked the driver to take me to the College Park airport. He had only a general idea of where it was. As we got closer, I noticed a Cessna in the airport traffic pattern. I loved being able to tell the cabbie, "Follow that plane!"

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    6. Thanks for not foisting the undignified and ironic current name of National Airport on us.

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    1. Yeah, we have been to Rocky Mountain Arsenal National Wildlife Refuge to hang out, but not for awhile. Hope the ecosystem is ok. . .

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    2. Another unhappy word from the range. I wonder if this happens regularly and we are only hearing about it now, or if the size and deadliness of the hail is an aberration?

      And speaking of killers, you better control Crazy Maizie.

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  8. Rockfall at Zion National Park on 8/24/19:

    https://youtu.be/3e8RpAEP1-A

    There were a few injuries but check out the bus outrunning the rockfall.

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    1. Just another scary part of nature. I tried not to think about that too much the last time I did the River Walk at Zion. You also think about a flash flood.

      Speaking of scary nature, the link from this morning's edition: breaches, screeches, where'd you get those leeches?

      Have you ever had a leech? I've only had very small ones, no African Queen drama. The ones I had were not really that scary, only about an inch long and the diameter of a pencil lead.

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    2. I worked with medicinal leeches in grad school. They have a ventral nerve cord consisting of a bunch of more or less identical ganglia, each with large, color-coded (well, at least identifiable) neurons. I'd stick glass micropipettes into neighboring neurons, and record the electrical activity, trying to figure out functional relationships.

      They don't have to eat very often, but they do have to bite through skin to suck blood. Couldn't convince undergrads to stick their hands into the tank, even for a 3-credit A. Couldn't bear to watch them desanguinate a frog after the first time. But, clean the lube off a sheepskin condom, fill it with expired blood from a local hospital, warm it up, and they're happy.

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    3. "clean the lube off a sheepskin condom, fill it with expired blood from a local hospital, warm it up, and they're happy." Just for the record, was it the leeches or the frogs or the undergrads who were happy?

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    4. Everybody except the sheep.

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    5. jan, ewe paint a picture!

      Thanks for that image.

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    6. Jan, do you have enough RAM to upload the image?

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  9. Sometimes extinction might not be a bad thing.

    The maple leaf on its back is obviously because that Canadian didn't want people to think it was from the US.

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    1. Wow, a 33-foot wingspan! I would have liked to see this critter flying about.

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    2. I agree, 3x the wingspan of an albatross (which I've never seen) or condor (which I may have seen) would be quite the site. I've flown in a Cessna 172 (VW Bug with wings) with a 36' wingspan.

      I think the WaPo article said that based on the size of its head and gullet, and lack of teeth, it likely scooped and fed on small mammals.

      Maizie might not have wanted to see this critter.

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    3. Maizie would likely have tried to make friends with this beast. . .

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  10. Today is the 6-year anniversary of Partial Ellipsis of the Sun! Thanks, especially, to jan, ecoarchitect, and Joanne for stopping by. Hoping to get a post out there this week!

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  11. Finally made it to the Ether Dome, and the rest of MGH's Museum of Medical History and Innovation. The main part of the museum is on the ground floor of a glass-walled building on a very busy street, but my wife and I were the only visitors to both while we were there yesterday afternoon. Can't imagine why this made anyone's Twelve Best list. Some pretty standard static displays of historical instruments and pictures of modern techniques, a video about research on hibernation and diving arctic mammals on continuous loop upstairs, and a nondescript roof garden. The Ether Dome itself is on the 4th floor of an old hospital building, on a silent corridor that's also labelled for Diabetes, Neuroendocrinology (which reminded me that I never caught my White Whale, a pheochromocytoma, during my admittedly brief career), and Inpatient Psychiatry. It's just an old-fashion operating theater, undistinguished but for its history and the anomalous presence of that mummy. The first-year students in the cheap seats up in the nosebleed section couldn't have been able to see much at all.

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  12. New post on "Machu Picchu: 15th Century Incan Sanctuary Purposely Built on Faults" is now up!

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