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Impact of sound on the brain

The impact of sound on the brain

Sound is capable of producing powerful reactions in the listener - whether it's a sudden cold sweat caused by a snake's warning hiss, or the uncontrollable grin as a favourite song from our youth comes on the radio. Scholars have been fascinated by the relationship between sound and emotional states since at least the time of the Ancient Greeks (whose wild Dionysian parties could be seen as the equivalent of a modern-day rave!), and modern neuroscience has led to some fascinating advances in our understanding of why our ears and emotions have such a strong bond.

Before we look at how sound affects us emotionally, let's quickly examine how it reaches our brains in the first place. Sound waves enter through the outer ear, before travelling through the ear canal to reach the eardrum. The eardrum then passes the vibrations through the middle ear bones (ossicles) into the inner ear or cochlea, which is filled with thousands of tiny hair cells. These hair cells are

what finally convert the vibrations into electrical signals, which are then sent to the brain through the hearing nerve.

All this explains how sound reaches the brain in a physical sense, but what about how the brain interprets different sounds?

Sound in the brain

Neuroscientists have linked a number of brain regions
with our emotional responses to sound. These include:

Thalamus - Relays sensory data and helps regulate sleep
Cerebellum - Refines motor functions and is associated with learning
Hippocampus - Inhibits behaviour and helps form memories
Amygdala - Processes memories and emotional reactions
Prefrontal cortex - Linked to personality and critical decision-making

Insular cortex - Regulates heartbeat and is connected to empathy, pain and social awareness Broca's area - Affects language comprehension and generation

A 2009 report from Sweden's Lund University put forward six psychological mechanisms through which emotions may be produced when the brain reacts to sound.

1) Brain stem reflex: When the acoustic characteristics of the sound (eg loud or dissonant) signal a "potentially important and urgent event", causing us to react on an instinctive level.

2) Evaluative conditioning: When an emotion is elicited by sound because we have heard it repeatedly in a certain setting, leading to an association between sound and setting.

3) Emotional contagion: When we perceive the emotion expressed by a piece of music: the music doesn't necessarily sound sad, but rather we recognise it as expressing sadness.

4) Visual imagery: When the structure of a piece of music makes us imagine certain scenes or sensations, such as a rising melody connecting with the sensation of moving upwards.

5) Episodic memory: Also known as the "Darling, they're playing our tune" phenomenon - when a particular sound or piece of music evokes a powerful memory.

6) Music expectancy: This is tied to our experiences with music: for instance, an unfamiliar variation on a standard note progression like may cause feelings of surprise and curiosity.

Of these mechanisms, the authors stated that the first two are in-born reactions, the second two develop during the first few years of our lives, and the last two tend to be learned during childhood and later life.

The amygdala and the sound of fear

This isn't the first time specific parts of the brain have been linked with sound memory. The amygdala - an almond-shaped region of the forebrain - has been proven a number of times to play a key role in fear conditioning. A classic (if rather cruel) experiment is to play a certain tone to a rat just before it is given an electric shock. Before long, the rat gives a fear response to the tone, as it has been conditioned to associate the sound with pain.

Joseph LeDoux, a postdoctoral student at the Medical College of Cornell University, performed experiments in the 1980s in which he removed various parts of rats' brains in a bid to determine where the response was generated. Removing the auditory cortex (the part of the brain where we first become aware of a sound) did not affect the rats' ability to learn the fear response. However, when he removed the auditory thalamus (the "relay station" that transmits the sound, before we become aware of it) the rats stopped learning.

LeDoux eventually pinpointed the amygdala as the region that is crucial to a learned fear response. The central nucleus of the amygdala has links to parts of the brain stem that control autonomic functions such as breathing and heart rate. Neuroscientists believe the amygdala may act as an 'alarm bell' for the brain, blasting out a fear warning in response to certain sights and sounds - sometimes before we are even fully aware they've happened.

Emotional communication

While language is a vital part of the way we communicate, it's not the only way we do it - the sounds and tones contained within language contribute a lot too.

A study carried out at the University of York's Department of Psychology in 2009 studied the effect of facial and vocal expressions on the brain, identifying a particular area of the brain that appears to be devoted to processing the two in tandem.

Using the university's magnetoencephalographic (MEG) scanner, the researchers tested the responses of participants to photographs of faces and recordings of voices. A region of the brain called the posterior

superior temporal sulcus showed high activity when participants were exposed to a "fearful" photograph and recording at the same time, but not when the faces or voices were neutral.

The findings suggest that this part of the brain may have developed to fulfil an important social function in humans, helping us to react not only to facial expressions but to read other cues such as tone of voice and body language.

Music and emotion

Music is capable of producing some of the strongest emotional reactions in humans, whether it's joy, sadness, fear or nostalgia. It's interesting to note than people from a diverse range of cultures and backgrounds will often agree on whether a piece of music sounds happy or sad - for this reason music is often considered the universal "language of emotions".

The idea of music as language is more accurate than it might first seem. When we hear music, our brains are imposing structure and order on a number of distinct sounds so that we experience them as a whole. It's a perceptual illusion that changes what we hear, much as we don't "hear" spoken language as a series of vocalisations - instead, we hear the meaning of the words.

However, music is much more rooted in primitive brain structures than language - structures connected with motivation, reward and primal emotions. For instance, that urge to get your shake on on the dance floor is caused by neural oscillators synchronising with the pulse of the music,

causing us to unconsciously anticipate when the next beat will occur. When the beat falls, our brains give us a small 'reward' hit for anticipating it correctly.

There's no strong scientific agreement on why music has such a powerful ability to conjure up the same images and feelings, even among different people with different memories. The appreciation of music involves a complex combination of the brain's memory, language, auditory and emotional centres all working together - perhaps it's simply this satisfying, harmonious brain-exercise that gives us the pleasure response.