How does music; a complete abstract stimulus, activate emotions? Music can be described as "organized sound", however, it communicates to us emotionally by unexpected violations in pitch, rhythm, meter, and tempo. Upon listening to music, the following brain structures are proposed to be activated: First, the auditory cortex in the superior temporal lobe for initial processing of sound. Second, frontal regions involved in processing musical structure and expectation. Third, limbic and paralimbic systems for emotion; accumulating with the activation of the nucleus accumbens at the experience of peak emotional responses to music. This region is involved in motivation and reward processing, and mediates the rewarding aspects of music by increasing dopamine levels. Throughout listening to music, the cerebellum, which is involved in the unconscious processing of rhythm and meter, is activated, and form connections to frontal regions as well as the limbic system.

Properties of music that generate emotions

The extent of the emotional responses of music depends on the structural features of music, as well as contextual features (such as the location one is while hearing the music, memories associated with the piece of music etc.). The difference between music and random noise has to do with how the relations of the following fundamental elements of music:
  • Pitch: a psychological construct related to the frequency of sound waves. Air molecules that vibrate slowly are associated with low pitch, and air molecules that vibrate quickly are associated with high pitch. Pitch is one of the primary means that musical emotions are conveyed. For example, a single high note can convey excitement, and a single low note can convey sadness.
  • Rhythm: the duration of a series of notes and how they are grouped into units.
  • Tempo: the speed of a piece of music
  • Timbre: distinguishes one instrument from another.
  • Loudness: a psychological construct relating to the amount of energy an instrument creates
  • Reverberation: the perception of how distant a sound is from us depending on how large the room the music is in.
All of these elements can be varied without altering one another [1]. When these elements combine, they give rise to meter, key, melody, and harmony.
Thus music can be described as "organized sound". However, organization is not enough to explain the generation of emotions.Too much organization (i.e. listening to scales) is boring. Rather, it is the unexpected violations in pitch, rhythm, melody, and harmony that allow music to communicate to us emotionally [2].

Perception of Music and Pitch in the Primary Auditory Cortex

Sound waves are detected by hair cells (primary auditory receptors) in the basilar membrane of the inner ear. The hair cells in the basilar membrane are frequency selective and form a tonotopic map: low frequency sounds excite hairs on one end of the basilar membrane and high frequency sounds on the other end. Complex sounds such as music will activate a broad range of hair cells. Signals from the basilar membrane are projected via the thalamus to the primary auditory cortex (A1), which is located in the superior temporal lobe. A1 as well, contains tonotopic maps containing high to low tones/pitches. Unlike other modalities, audition is unique in that pitch is directly represented in the brain [3]. For example, if experimenters were to place electrodes in the auditory cortex, it is possible to determine what pitch is being played by looking at brain activity [1].


Chords and Harmony

A chords is a group of (usually three or more) notes played together, and is what composers use to create the "mood" of a piece of music. Both musicians and nonmusicians alike produce different physiological responses to major versus minor chords. Major chords are generally associated by positive, happy effects; whereas minor chords tend to increase levels of calmness, as well as sadness [4].
Harmony is the way different chords are strung together; and the way particular notes combine produces different emotions.
Dissonance is generally referred to as a combination of notes that sound unpleasant or unstable; whereas consonance refers to chords that sound pleasant or harmonious. One of the most dissonant musical intervals is the tritone, which is the musical interval of an augmented fourth (the distance between C and F-sharp). This interval was considered so dissonant that it was banned by Church, and named "Diabolus in musica" or the devil in music [1].


Unconscious Interference, Feature Extraction, and Feature Integration

While listening to music, we do not consciously perceive individual harmonics of a particular instrument. Instead, our brains are can analyze dozens of different frequencies encoded by the auditory cortex, and piece them together to create the illusion that we are listening to a single sound. This process is called "unconscious interference" [5], and is carried out by two processes: a bottom-up process of feature integration and a top-down process of feature extraction.

Feature Extraction

Lower level, bottom-up processing occurs in phylogenetically older brain areas including the cochlea, auditory cortex, brain stem and cerebellum; and involves extracting features such pitch, timbre, rhythm, loudness etc. in parallel, by neural circuits that are able to operate independantly of one another.

Feature Integration

High level, top-bottom processing occurs in the newer areas of the brain such as the frontal cortex, which integrates extracted information processed from lower level structure. Furthermore, based on the piece of music being listened to as well as memories of music that sound familiar to the music currently being listened to, these areas are involved in predicting what is to come next.


Musical Structure and Expectation

Sequences of notes themselves are not enough to affect us emotionally. Rather, our ability to connect to music emotionally depends on experience, culture, and brain structures that are modified every time one listens to a new song, or re-listens to an old song [1].
For example, another aspect of music that that greatly affects our emotional response is rhythm. Physically and emotionally moving music more than often contains a readily predictable beat. In order for the brain to detect changes in rhythm and beat, it must have a system that is able to extract when beats are supposed to occur. This is called metrical extraction. Lesion studies have shown that rhythm extraction, metrical extraction, and the perception of melodies all occur in distinct brain regions. Patients with damage to the left hemisphere cannot perceive rhythm but can extract meter, whereas patients with damage to the right hemisphere can perceive rhythm but cannot extract meter [6]. On the other hand, right temporal lobe lesions impair the ability to perceive melodies [7]. The primary auditory cortex connects to the frontal lobe, the area that is involved with processing musical structure. This area analyzes the temporal patterning of the music. In particular, the prefrontal cortex is the region in which expectation is created; and where violation and satisfaction of expectations occur [3].

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Regions of the brain involved in the perception of music. Tramo (2001)




Neural correlates of music generated emotions: Evidence from Imaging Studies

Limbic and Paralimbic Structures

Almost all limbic and paralimbic brain structures have been shown to be modulated upon listening to music [8].
Studies using PET have shown that intense musicalal emotion directly correlates with brain areas involved in reward, emotion, and arousal. These intense musical emotions are known as "musical chills", involve goosebumps or shivers down the spine. Participants experienced these chills while listening to their favourite songs, and brain areas activated upon these chills included the amygdala, ventral striatum, midbrain, amygdala, orbitofrontal cortex, and ventral medial prefrontal cortex [9]. Another study investigated the neural correlates of unpleasant melodies and found activation within the posterior cingulate cortex is activated, an area involved in conflict or emotional pain [4].
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Regions demonstrating significant rCBF correlations with chills intensity ratings. Figure from Blood et al. (2001)




Amygdala and Hippocampus

The amygdala, the primary emotional center of the brain, is activated upon listening to music, but not activated upon listening to random noise[8]. The amygdala is highly involved in emotional memories. Therefore, it is likely the case that the amygdala is involved in emotional memories envoked upon listening to music. Studies involving the amygdala have shown activation in the amygdala whie listening to both pleasant and fearful/unpleasant music [10].

Many studies have reported activity in the anterior hippocampus upon listening to music [8]. The hippocampus is the area of the brain involved in learning and memory, and seems to be important for memories envoked by listening to music. However, one study reported hippocampal activity both when participants listening to familiar and unfamiliar music [8]. It might be the case that the hippocampus is not only involved in memory, but is also very important for emotional processes. The hippocampus contains connections to both cortical and subcortical regions, including the hypothalamus (for regulating autonomic and hormonal activity), amygdala, thalamic nuclei, cingulate gyrus, insula, and autonomic brain stem nuclei; and thus seems to be an integral region for emotion.

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Neural correlates of music processing. Levitin (2006).

Frontal Regions

EEG studies have found that overall, frontal lobe activity increases as musical stimuli become more intense. Furthermore, regarding valence (i.e. positive vs. negative elements of music), fearful and sad musical segments are associated with increases in right frontal EEG activity, while joyful musical segments are associated with increases in left EEG activity [11].

Cerebellum

The cerebellum, the part of the brain involved in timing and coordinating movement, is involved in the processing of rhythm and meter, and tracking the beat. It a brain region that is important to the emotional aspects of music. Studies have shown activation of the cerebellum upon listening to music, but not upon listening to random noise [12]. Furthermore, neuroimaging has shown that the cerebellum is activated when participants listen to music that they like versus music that they don't like. Additionally, the cerebellum contributes to regulate emotion through its connections to both limbic areas (such as the amygdala which is involved in emotional memories), and the frontal lobe (which is involved in planning) [1].

Further evidence that supports the role of the cerebellum in processing emotion in music relates to two genetic disorders: Williams syndrome (WS) and Autism Spectrum Disorders (ASD).
Williams syndrome is a genetic disorder that causes abnormal neuronal and cognitive development. However people with Williams syndrome tend to be highly social, as well as very good at music. On the other hand, people with autism spectrum disorders are highly unsocial, and tend to lack the abil
ity to understand emotions. Furthermore,its is reported that people with ASD are not usually emotionally moved by music. There thus seems to be a connection between musical emotions and sociability. There appears to be a double dissociation in the brain regions affected in these disorders: the neocerebellum tends to be larger in people with WS and smaller in people with ASD, providing further evidence that the cerebellum is important in processing emotion in music [13].


Music, Motivation, and the Dopaminergic system

An early study in the 1980s showed that the pleasurable aspects of listening to music could be blocked by administrating a drug called nalaxone, which appears to interfere with dopamine in the nucleus accumbens [14]. However, direct evidence of the involvement of the nucleus accumbens and music has only been demonstrated within the past couple of years. Activation of the limbic system in response to listening to music culminates in the activation of the Nucleus Accumbens, in which studies have shown occurs during the experience of peak emotional responses to music. The nucleus accumbens is involved in motivation and reward processing, which mediates the rewarding aspects of music by increasing levels of dopamine. A recent study by Valorie Salimpoor and colleagues used positron emission tomography to show that the endogenous release of dopamine occurs at the ventral striatum at peak emotional arousal during listening to music. Furthermore, functional magnetic imaging demonstrated that the caudate nucleus is involved in anticipation and the nucleus accumbens is involved during the peak emotional response to music. These results indicate that pleasure in response to music leads to dopamine release in the striatal system. Thus, this may explain the rewarding, as well as addicting, aspects of listening to music [15].
It has also been demonstrated that along with activation of the nucleus accumbens and the ventral striatum, the hypothalamus is highly activated upon listening to pleasant music. The hypothalamus is the area of the brain involved in autonomic responses including heart rate and respiration; and listening to pleasant music is accompanied by changes in these regions. Furthermore, functional connectivity analysis has shown high correlation between the nucleus accumbens and the hypothalamus. Therefore it may be the case that the nucleus accumbens and hypothalamus work together mediate feelings of reward upon listening to music [16].


See Also




References


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2. Krumhansl, (2002). Music: A link between cognition and emotion. Current Directions in Psychological Science 11 (2):45-50

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4. Kratus, J. (1993). A developmental study of children's interpretation of emotion in music. Psychology of Music, 21, 3-19.

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15. Valorie Salimpoor, Mitchel Benovoy, Kevin Larcher, Alain Larcher, and Robert J Zatorre (2011) “Anatomically distinct dopamine release during anticipation and experience of peak emotion to music” Nature Neuroscience. 14: 257 -262

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