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.
