I hope you all are ready to help me welcome #NeuroThursday back in action this week with a story about how you stay balanced - and the amazing things you accomplish with that ability!
This topic was requested by the illustrious @KJKabza, who wondered: "Are there special strengths of the human balance system (we all know that it is easily disrupted if you spin around)?"
Yes, KJ, oh yes. Your balance system is doing highly badass things all the time, quietly under the hood while you go about your life. Like the devil, its best trick is making you think it's not even there.
So what is this balance system? Mostly it's the "vestibular system," a set of tiny organs in your inner ear that detect movement of your head. Neaby the ear-bits that pick up sound, but distinct.
(For non-head balance, you have another sense, called proprioception - a distributed sensory system that detects your body position. But that could be a topic for another day!)
This handy Wikipedia image shows the layout well. The important parts are the Semicircular Canals/Ducts (3 rings in the organ's upper-left) and the Utricle and Saccule (blobs in middle). The snaily bit below is for hearing.
The semicircular canal & utricle/saccule all follow the same principles. They're filled with Goop, and when the goop moves, it bends tiny hair cells. The hair cells are neurons, and they activate when bent. Bam!
How the canals work: imagine spinning a hula hoop full of water - the water lags behind a bit. The hair cells are attached to the rim, so from their little POV the water is flowing past them, and they bend in the current.
These canals are for detecting rotation: if I just shove my hula hoop around (instead of spinning), it's not gonna work. You have multiple canals in different orientations so that you can detect head rotation in any direction.
The semicircular canals are the part that get out of whack if you spin around too much! Put too much velocity in the water and it'll keep going and going and going even after you stop spinning the hula hoop.
The utricle/saccule are simpler. Goop is full of tiny crystals. Linear acceleration will jostle the crystals & thus the hair cells.
Whew that's enough anatomy. But now you know how we detect head motion. Ok please stand up and spin around until you understand this system's flaws. I'll wait.
Seeing straight yet? No rush, I'll be here. C'mon! You know you want to!
Okay anyways. Now you definitely know the flaws in this system. But it's allowed to have some flaws because it is SO GOOD. Let us demonstrate. (No seasickness this time, promise.)
You can do the demo with this text if you're reading on a laptop/phone. If you're twitterizing from a desktop computer, grab a book.
As you read this tweet, shake your head back and forth. Start slow, as if saying "no thanks" to this demo, then build up speed. You should be able to move pretty fast and still read this tweet.
Now hold your head still, and shift your screen back and forth instead.
Hahaha no you can NOT read while your screen/book is shaking back and forth. Why the difference? VESTIBULAR SYSTEM, BABY.
Down in your brainstem, your vestibular system connects to your eye-movement system. That connection lets your eyes compensate automatically for your head movements.
If this were easy to do, you could read while shaking your book! But it's gotta be perfect, and you can't pull that off alone.
If you want to be a goofball, test this in the mirror. Watch your eyes while you move your head around! You can hit a limit somewhere, but generally it's a perfect match.
This is your vestibular system's magic: it lets you tell what head movements you make, and compensate for them to keep your visual field fixed. Super useful for every activity that involves looking at things without holding your head stock-still.
Which is, really, most things. But if you wanna invent an evolutionary explanation, we can spin a story about keeping that visual field unmoving so you can detect actual real motion in the world.
When this system goes wrong, you get a condition called nystagmus: uncontrolled movements of the eyes, as if it always thought you were aspin. Awesome creepy video ahoy!
So here's your #NeuroThursday takeaway: your balance system is SO GOOD, you never notice all the hard awesome work it does keeping your gaze where you want it.
(And by "you," I mean the typical human. Maybe not you personally! That's cool, you do you! But if not you, maybe ask your doctor – or check out the Vestibular Disorder Association vestibular.org )

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More from @BenCKinney

Jul 8, 2021
Welcome to this week's edition of, "I'm a neuroscientist, and this thread is spot on."

Physical limits, including strength, are a brain game.
A classic (apocryphal?) study: tell people to bike as fast as they can. Let them see their RPM meter.

Make 'em do it again - but tweak the RPM meter so it reads low. And they'll blow past their original "as fast as they can" to make the (apparent) RPM match.
An even better illustration of this effect is in stroke patients. One common side effect of stroke is hemiparesis - weakness on one side of the body.

But wait. Why does brain damage cause muscle weakness?
Read 10 tweets
Jul 1, 2021
As a neuroscientist who studies handedness: this is spot on.

Handedness is congenital, not learned. But the frequency of left-handedness varies between cultures - in a way that almost certainly reflects social acceptance, not heredity.
The most interesting data on this come from China. Most East Asian cultures have a lower prevalence of left-handedness than Europeans. But, again, this is not genetic. How do we know? Hong Kong.
Globally, left hand preference runs about 10%. Based on studies of art history, this value is pretty much stable across continents and millennia. I went into detail on the deep historical data in this ol' thread. benjaminckinney.com/handedness-acr…
Read 15 tweets
Dec 14, 2020
In case anyone had doubts that @/longshotpress was a bad actor, they doxxed me today.

I'm not afraid of them. My boss knows I do this. But do you think ANYONE should submit to a publisher who'll track down your real name & address, and publish it online, if you criticize them? Screenshot of Longshot Pres...
If you're new to this whole disaster, I've tracked Longshot's asshattery via this post here, ever since it started in February. Feel free to report 'em, of course. (And let me ping @victoriastrauss for this new round of misbehavior.) benjaminckinney.com/writer-warning…
Now that their original tweet is gone: in case it isn’t obvious, I added all those grey boxes myself. Mr. White posted my contact info in full.
Read 4 tweets
Oct 19, 2019
Alright, #sciencefiction #neuroscience fans: this is the content you’re here for! In ~30 minutes, I will livetweet this #sfn19 “Dialogues Between Neuroscience & Society” talk on the future of AI and machine learning in human society. Bio of speaker Fei-Fei Li for “dialogues between neruoscience & society” talk
Any minute now we should be underway with the #SfN19 Dialogues Between Neuroscience and Society talk by @drfeifei on how AI can - and should - change the human experience. Stay turned for livetweeting!
Yes, it is 11:10. No, the talk has not started. We haven’t even begun introductions yet. Stay patient, friends!
Read 75 tweets
Jun 20, 2019
Inhale deeply, and enjoy the aroma of #NeuroThursday, because this week I want to talk about smell, taste, and emotion – inspired by @tinaconnolly's Nebula- and Hugo-finalist novelette, "The Last Banquet of Temporal Confections." A perfume bottle, labeled
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. tor.com/2018/07/11/the…
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?
Read 28 tweets
Jun 15, 2019
Let me know if y’all want a neuroscience on this!
So a very quick #neuroscience on this: initial visual processing in the brain (and retina) works through contrasts. Your brain sharpens differences/edges because that’s where information is...
Your neurons are tuned to heighten/inhibit each other in a way that magnifies differences. So when a neutral color goes up next to red, your brain magnifies that difference and makes the neutral seem as not-red as possible.
Read 6 tweets

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