How the brain hears and fears?

How is it that a sound can send a chill down your spine?


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Music has the potential to immensely affecting and alter the moods, actions, and decisions of people. Not only for humans, but also for animals, music start dancing, moving and acting a bit strange.

However, have you ever noticed that there are certain kinds of sounds, especially in horror movies, that give you the chills and have the potential to rob you of your sleep? Why do these sound seem so scary?

A new study on individual brain cells of mice, scientists now have a better understanding of how a sound can incite fear.

Scientists focus on a part of the mouse brain called the amygdala where sights, sounds, and other stimuli take on positive or negative associations through experience. The continuous process of learning and unlearning that occurs in the amygdala appears impaired in people with anxiety disorders or major depression. Understanding brain cell or neuron activity in the amygdala could result in better treatments.

Scientists detected profound changes in neuron activity when they trained animals to fear a particular sound and associate another sound with a reward.

Investigator Bo Li said, “If you look at the patterns of brain cell activity in the amygdala, you can know whether the animal is expecting a reward or fearing a punishment.”

Scientists used a microscope with a lens small enough to implant in the brain of a mouse, to track the firing activity of specific neurons before, during, and after an animal’s training.

They taught the animals to associate particular sounds with reward or punishment and saw the behavior of neurons evolve. The experiment associated one tone with an annoying puff of air–the punishment. The reward tone was a refreshing drop of water to drink.

At first, neurons sensitive to sound responded to each tone by firing randomly. But when one tone was repeatedly accompanied by the puff of air, the neurons fired in a very specific pattern. This pattern closely resembled the firing pattern of another type of brain cell that fires when the mouse actually experienced the punishment. Likewise, when a tone was repeatedly paired with a sip of water, the sound-sensitive neurons fired in a pattern similar to neuron activity when the mouse received the water reward.

As the firing patterns turned out to be more explicit, the animals licked because of the reward-associated tone- -anticipating water. They flickered in light of the punishment related sound- – associated an air puff.

The analysts likewise exchanged the importance of each tone. At the point when the reward sound was over and over joined by an air puff, the neurons let go of the built-up reward terminating design and embraced the punishment pattern.

Li said, “We think this is how sound acquires meaning.”

The study is published in the journal Nature Communications.