Category Archives: NeuroThursday

Smell, Taste, and Emotion

NeuroThursday is wafting by this week for a piece on smell, taste, and emotion! The full text is posted here, below the Twitter link. You can also find a ThreadReader version at the very bottom.

Inhale deeply, and enjoy the aroma of #NeuroThursday, because this week I want to talk about smell, taste, and emotion – inspired by Tina Connolly‘s Nebula- and Hugo-finalist novelette, “The Last Banquet of Temporal Confections.”

If you haven’t read it, it’s a wonderful story about memory, food, cruelty, and empathy. But you don’t need to read it for this thread. I’m here to talk about neuroscience, not pastry-magic. https://www.tor.com/2018/07/11/the-last-banquet-of-temporal-confections-tina-connolly/

Tastes and smells are notoriously emotional. Smells can evoke a flood of memories, with all their associations. Freshly-cut grass, your partner’s favorite flowers, the spices of your favorite meal, or the ammoniac strike of a campground toilet. Why so strong?

The first step is to realize that by “taste and smell,” we’re really just talking about smell. Most of the experience you get when enjoying food – the stuff we think of as “taste” – comes from the nose, not the tongue.

(Try eating with your nose clamped shut. Or don’t. It’s terrible.)

So now we’re talking just about smell. This sense works via 10-20 million olfactory neurons (labeled in image as “receptor cell”). They’re embedded in “olfactory epithelium” at the roof of your nose. (Epithelium = body’s surface layers, whether skin or a hollow space.)

Olfactory Neurons & Epithelium

Each of those neurons has one type of “olfactory receptor,” which does the scent detection itself. One receptor type, but many copies of it.

A scent enters your nose, dissolves into the mucus in there (appetizing!), and thus reaches olfactory receptors. When a receptor matches the scent, the two molecules will bond. Ions flow into the neuron, and a signal is produced.

Olfactory receptors are incredibly diverse. 900+ genes (the largest gene family in the body), and each receptor is broadly tuned so it can detect more than one scent. Like the visual receptors in the eye, which I discussed on a NeuroThursday past.

In the eye, your “red” cones respond strongest to red light, but respond medium-strongly to wavelengths close for red. Same idea in the nose: each receptor can respond medium-well to scents with similar molecular shapes.

This is why scents *mean* things. If two molecules are related (with common features), they’ll bond to the same receptors (though not at equal strength). Same receptors = similar info to your brain = similar smell!

As with the eyes, broad tuning – a neuron has one target, but responds weakly to near-misses– is the way to perceive structure in the world.

This is super-fundamental, preserved across evolution. Olfactory neurons have basically the same cellular and molecular properties across all animals.

So now that we understand the biology of smell, we’re ready to ask why they’re so emotionally powerful.

Most of those emotional associations are learned: with exposure, we’ve learned that swimming-pool-chlorine tastes like summer. This can, in turn, bring up a specific summer-pool memory.

(There are exceptions to this “learned” thing – particularly in the realm of disgust, which starts as a hardwired thing. But even there, learning & association add layers.)

But smell memories can be more emotionally vivid than others. Is there something special about smell and emotion?

We have ideas, but no solid answers. “Emotional memory strength” isn’t exactly something modern science can study effectively. But the anatomy does point toward a possible explanation.

Those little olfactory neurons are rooted in your Olfactory Bulb, which does some initial processing of olfactory information, and receives guidance from top-down stuff like attention.

Olfactory Bulb image

The olfactory bulb is part of your brain, and it connects straight to the limbic system: a network of areas in the brain involved in emotion and the formation of memories.

Some well-known parts of the limbic system could deserve their own NeuroThursday, since there are a lot of misunderstandings about them. If you know what the “hippocampus” is, I’d say 30% odds you know something false.

But the point here is that the olfactory bulb has direct access to parts of the brain involved in emotion and memory. One possible #NeuroThursday takeaway is that, yes, there’s an anatomical basis for smell memories to be uniquely evocative.

However, I’d like to finish by pivoting from fact to opinion. (Can your olfactory neurons detect the rank smell of punditry?)

Smell can be highly emotional. But so can vision and hearing. The sight of a loved one, the sound of a familiar song. Even a gentle touch, at the right time, can produce a mighty emotional response.

I’m not 100% convinced that there’s anything uniquely emotional about smell, compared to our other senses. Maybe its emotional-intensity only stands out because we don’t think about smell as often: we needed to be reminded of its intensity.

Powerful memories and delicious scents may make a challenging research project, but they’re a deep (and hopefully delicious) part of our lives, whether or not we pay attention to them.

Did you enjoy the scent of this #NeuroThursday on taste, smell, and emotion? Share it around, or check out some of my fiction! And if you haven’t yet read Tina’s story above, now’s the time!


Threadreader version:

https://threadreaderapp.com/thread/1141845165142958080.html

Impending Doom

It may not be Thursday, but I found a good excuse to go all neuroscience on the experience described in the medical literature as “Sense of Impending Doom.”

Twitter:

Or on the web via Threadreader App!

2018 in Review & Awards Eligibility

Another year is coming to a close, and much to show for it, ups and downs and every direction. I finished the first draft of a new novel, and worked on more short stories than I can shake a metaphor at. I made the Campbell Award longlist! I lost a Hugo award with the rest of the amazing Escape Pod team, and took part as we won and rejected a Parsec award. My final submission to Writers of the Future became a finalist, but I withdrew my story over ethical concerns. I sold 4 original stories, but two of those sales fell through when the magazines closed.

I had five original stories come out in 2018. In chronological order:

  1. Toward Lands Uncharted – Mind Candy, Feb 2018 (secondary world fantasy, 4900 words). A diplomat and spy must try to save her nation and its very history from their conqueror’s Sykes-Picot border magic.
  2. Where the Anchor Lies – Beneath Ceaseless Skies, Feb 2018 (science fantasy, 4000 words). A general visits the grave of the sentient battleship she loved, to use it as a political tool.
  3. The Seeds We Plant – Compelling SF special issue, Sep 2018 (science fiction, 2200 words). When a colony ship suffers a brutal accident, the pilot must reply on his emotional-control neuroprosthesis to save his cargo.
    • Not available free online. Contact me for a copy in the format of your choice.
  4. Elegy of Carbon – The Internet Is Where The Robots Live Now, Nov 2018 (science fiction, 4100 words). In the waning days of the solar system, a mining AI must find a new way to fulfill the purpose it loves.1
    • Not available free online. Contact me for a copy in the format of your choice.
  5. The Hammer’s Prayer – Diabolical Plots, Dec 2018 (contemporary fantasy, 3300 words). A golem hides away in ugly places, to help him resist the compulsion to share his gift of animation.2
    • If you only have time to read one story, this is the one I recommend.

I didn’t have much time for nonfiction this year, but I did publish:

  1. The chapter “What’s Possible with Cyborgs and Cybernetics” in Putting the Science in Fiction (Writer’s Digest Books). I’m also quite proud of my associated writing-prompts post, “Machines, You, and Other Synonyms.”
    • Putting the Science in Fiction – a collection of 59 essays by scientists and other experts, designed to help authors write with authenticity – is eligible for the Hugo award for Best Related Work .
  2. Twelve new entries in the #NeuroThursday Twitter feature.

If you’re in a position to nominate for awards of any kind, I hope you’ll consider not only these fine works, but the whole team over at Escape Pod. We work hard every week to bring you the finest in audio fiction, and we’ll be eligible once again for the Hugo Award for Best Semiprozine. We also published a lot of awesome stories, so take a look back at that list and see if one of them feels worthy of your love too!

Meaningful Knowledge and Dopamine

NeuroThursday takes a hiatus from its hiatus this week! Read on through to see how a recent article about dopamine in beliefs can get us thinking about what’s meaningful, and what we do with the meaning we detect in our lives.

Twitter:

Threadreader:

https://threadreaderapp.com/thread/1050555234282590208.html

Motion Illusions and Adaptation

I don’t care if it’s Tuesday! Linear time bends to my whim, and we have a NeuroThursday on the ubiquitous “motion aftereffect” illusion, and the cellular properties that cause it!

Twitter:

Threadreader page:

https://threadreaderapp.com/thread/1014328050287247360.html

Synesthesia & Evolutionary Psychology

NeuroThursday reappeared this week in a flash of numbers and sound, to tell us about synesthesia! The condition, and its implications for how we think about human evolution.

Twitter thread:

Thread Reader page:

https://threadreaderapp.com/thread/1007413448647561216.html

Yanni, Laurel, and McGurk: Auditory Illusions

NeuroThursday this week is on auditory illusions, as inspired by Yanni/Laurel!

ThreadReader:

https://threadreaderapp.com/thread/997278732493746182.html

Twitter:

Two Spaces of Analysis

NeuroThursday took some unexpected (to me) twists and turns this week, as a piece about that silly “two spaces are better!” article turned into an object lesson on the challenges of scientific analysis!

Thread Reader

https://threadreaderapp.com/thread/994760033224286208.html

Twitter

Body Position

NeuroThursday is stumbling on through with a second piece on balance: this time, the “proprioceptive” senses your body uses to keep track of its own position.

Threadreader link

https://threadreaderapp.com/thread/989660943826202624.html

Twitter thread

Badass Balance

NeuroThursday returns this week with a tale about all the secret badassery of your balance (vestibular) system!

Threadreader

https://threadreaderapp.com/thread/982049016857972738.html

Twitter thread