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Why Is the Sound of Nails on a Chalkboard So Unpleasant?

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The act of scraping nails down a chalkboard creates a sound so awful that most people have an instantaneous reaction: A shiver runs up the spine, and they slap their hands over their ears. Anything to block out that noise! But why do unpleasant sounds affect us like this?

Newcastle University scientists think they’ve pinpointed why. For a new study , the researchers placed 13 subjects inside functional Magnetic Resonance Imaging (fMRI) machines, which measure brain activity by detecting changes in blood flow. As they played a range of 74 sounds, the scientists watched what happened in the brain.

They found we recoil from unpleasant sounds because of the interaction between two areas of the brain: The auditory cortex, which processes sound, and the amygdala, which is active when we process negative emotions. So when someone screams, or a baby cries, the amygdala takes over, heightening the activity in the auditory complex and creating a negative reaction. This activity is not as heightened when listening to a soothing sound.

Based on acoustic analysis, the scientists determined that all sounds from 2000 to 5000 Hertz were unpleasant to the subjects of the study. They hope that a better understanding of how the brain reacts to noise will help people sensitive to loud sounds, like those with some forms of autism, and people who suffer from tinnitus and migraines.

But perhaps the most surprising thing to come out of this study is that the subjects rated nails on a chalkboard the fifth most irritating sound—knife on a bottle, fork on a glass, chalk on a blackboard and ruler on a bottle all come before it.

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Big Questions
What Is the Difference Between Generic and Name Brand Ibuprofen?
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What is the difference between generic ibuprofen vs. name brands?

Yali Friedman:

I just published a paper that answers this question: Are Generic Drugs Less Safe than their Branded Equivalents?

Here’s the tl;dr version:

Generic drugs are versions of drugs made by companies other than the company which originally developed the drug.

To gain FDA approval, a generic drug must:

  • Contain the same active ingredients as the innovator drug (inactive ingredients may vary)
  • Be identical in strength, dosage form, and route of administration
  • Have the same use indications
  • Be bioequivalent
  • Meet the same batch requirements for identity, strength, purity, and quality
  • Be manufactured under the same strict standards of FDA's good manufacturing practice regulations required for innovator products

I hope you found this answer useful. Feel free to reach out at www.thinkbiotech.com. For more on generic drugs, you can see our resources and whitepapers at Pharmaceutical strategic guidance and whitepapers

This post originally appeared on Quora. Click here to view.

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Big Questions
Do Cats Fart?
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Certain philosophical questions can invade even the most disciplined of minds. Do aliens exist? Can a soul ever be measured? Do cats fart?

While the latter may not have weighed heavily on some of history’s great brains, it’s certainly no less deserving of an answer. And in contrast to existential queries, there’s a pretty definitive response: Yes, they do. We just don’t really hear it.

According to veterinarians who have realized their job sometimes involves answering inane questions about animals passing gas, cats have all the biological hardware necessary for a fart: a gastrointestinal system and an anus. When excess air builds up as a result of gulping breaths or gut bacteria, a pungent cloud will be released from their rear ends. Smell a kitten’s butt sometime and you’ll walk away convinced that cats fart.

The discretion, or lack of audible farts, is probably due to the fact that cats don’t gulp their food like dogs do, leading to less air accumulating in their digestive tract.

So, yes, cats do fart. But they do it with the same grace and stealth they use to approach everything else. Think about that the next time you blame the dog.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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