The painful squeal of chalk on a blackboard

#ds31 - Nails on a Chalk Board

The squeal of chalk on a blackboard” feels painful to almost everyone.   Scientists speculate that nails screeching on a blackboard sounds like primate distress calls.

But for many people with sensory processing difficulties, the hiss of running water or the roar of a vacuum cleaner can sound just as unpleasant as nails on a blackboad.   So maybe it makes sense to look at just how typical brains decide nails on the chalkboard is such a painful sound.  Maybe the same equipment is involved in autistic sensory pain to noises.

To learn about the processing of painful (“aversive”) sounds, we turn to:

A Dynamic System for the Analysis of Acoustic Features and Valence of Aversive Sounds in the Human Brain

Sukhbinder Kumar, Katharina von Kriegstein, Karl J. Friston,and Timothy D. Griffiths

Researchers had previously found that a spectral analysis of a sound could predict its relative unpleasantness.   Now they embarked on an even greater adventure — to see if this spectral analysis could be used to predict functional MRI data of people listening to painful sounds.

Dynamic Causal Modeling of misophonia 2

First fMRI was acquired from 13 subjects as they listened to 74 different sounds.  Subjects rated each sound on its unpleasantness.

Analysis revealed activity in both amygdala were correlated to the acoustic features, but only the  right basolateral amygdala was found to be correlated to the unpleasantness of the sound.  The authors discuss how the basolateral nucleus acts as the amygdala’s “sensory interface”, receiving signals from the both the auditory thalamus and the association areas of the auditory cortex“.

Acoustic features correlated with activity in the auditory cortex (specifically the anterior Superior Temporal Gyrus and the “upper bank” of the Superior Temporal Sulcus).     The unpleasantness of the sound was correlated only with the right Superior Temporal Gyrus.

Dynamic Causal Modeling of misophonia 1
Red = Acoustic features , Blue = Valence

 

Researchers conclude that the audio signal is first processed  in the auditory cortex (superior temporal gyrus), after which it is passed to the amygdala which evaluates the signal’s unpleasantness.    That value judgment is the passed back to the auditory cortex.

Why do the vacuum cleaners or showers elicit fear or pain in people with sensory issues? If it’s for similar reasons to chalkboard scraping, then perhaps we should look to the right basolateral amygdala.

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The Old Woman, the Pig, Chain-Anxieties and racing thoughts

When I was young, I loved Chain-Stories like “The Old Woman and Her Pig“.   The protagonist has a goal which leads to a conflict, an obstacle

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An old woman was sweeping her house, and she found a little crooked sixpence. “What,” said she, “shall I do with this little sixpence? I will go to market, and buy a little pig.”

As she was coming home, she came to a stile. But the piggy wouldn’t go over the stile.

Attempts to solve the first problem only lead to a second problem:

She went a little further, and she met a dog. So she said to him, “Dog! Dog! Bite pig. Piggy won’t go over the stile; and I shan’t get home tonight.” But the dog wouldn’t.

Soon the problems have piled up, one after another  after the another:

She went a little further, and she met a stick. So she said, “Stick! Stick! Beat dog! Dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.” But the stick wouldn’t.

She went a little further, and she met a fire. So she said, “Fire! Fire! Burn stick. Stick won’t beat dog; dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.” But the fire wouldn’t.

She went a little further, and she met some water. So she said, “Water! Water! Quench fire. Fire won’t burn stick; stick won’t beat dog; dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.” But the water wouldn’t.

She went a little further, and she met an ox. So she said, “Ox! Ox! Drink water. Water won’t quench fire; fire won’t burn stick; stick won’t beat dog; dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.” But the ox wouldn’t. She went a little further and she met a butcher. So she said, “Butcher! Butcher! Kill ox. Ox won’t drink water; water won’t quench fire; fire won’t burn stick; stick won’t beat dog; dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.” But the butcher wouldn’t.

She went a little further, and she met a rope. So she said, “Rope! Rope! Hang butcher. Butcher won’t kill ox; ox won’t drink water; water won’t quench fire; fire won’t burn stick; stick won’t beat dog; dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.” But the rope wouldn’t.

She went a little further, and she met a rat. So she said, “Rat! Rat! Gnaw rope. Rope won’t hang butcher, butcher won’t kill ox; ox won’t drink water; water won’t quench fire; fire won’t burn stick; stick won’t beat dog; dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.” But the rat wouldn’t.

She went a little further, and she met a cat. So she said, “Cat! Cat! Kill rat. Rat won’t gnaw rope; rope won’t hang butcher; butcher won’t kill ox; ox won’t drink water; water won’t quench fire; fire won’t burn stick; stick won’t beat dog; dog won’t bite pig; piggy won’t get over the stile; and I shan’t get home tonight.”

But the cat said to her, “If you will go to yonder cow, and fetch me a saucer of milk, I will kill the rat.” So away went the old woman to the cow.

Racing thoughts can be like that.   One obstacle or anxiety leads to a whole chain of problems and anxieties.  Sometimes these lead to paralysis – a giant Gordian Knot with no clear loose ends, no where to begin.

It’s easy to give into despair and paralysis in these moments.     And no-win scenarios do exist.

But sometimes, there are elegant solutions that resolve problems that felt  completely unsolvable:

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But the cow said to her, “If you will go to yonder haystack, and fetch me a handful of hay, I’ll give you the milk.” So away went the old woman to the hay-stack; and she brought the hay to the cow.

As soon as the cow had eaten the hay, she gave the old woman the milk; and away she went with it in a saucer to the cat.

As soon as the cat had lapped up the milk, the cat began to kill the rat; the rat began to gnaw the rope; the rope began to hang the butcher; the butcher began to kill the ox; the ox began to drink the water; the water began to quench the fire; the fire began to burn the stick; the stick began to beat the dog; the dog began to bite the pig; the little pig in a fright jumped over the stile; and so the old woman got home that night.

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How topical anesthetics can beat needle stick pain

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If you don’t have sensory issues, maybe you don’t mind getting blood drawn.  But for those of us with sensory issues, the phlebotomist is a source of dread.

Now help is on the way.

Your local pharmacy probably stocks all manner of topical anesthetics, usually marketed at Toothache Relief products with names like Orajel.    These gels and liquids contain 10-20% Benzocaine (or a similar anesthetic).

Next time you are dreading a blood draw or a flu shot, buy some topical anesthetic and apply it to the site you’re about to get stuck, and say goodbye to needlestick pains.