Our brain processes music simultaneously in a systematic and distributed manner (Levitin, 2007; Weinberger, 2004); it does not possess a localized "music center." Rather, listening to music activates several areas of the brain associated with different cognitive responses (Weinberger, 2004). When we listen to music, the sound waves enter our ears and are converted into fluid waves by the external and middle ear. These fluid waves enter the inner ear (i.e., the cochlea) and trigger the vibrations of the inner ear hair cells, which in turn generate electrical signals (Kalat, 2010). These cells then transmit electrical signals to other areas of the brain that are involved in further processing and analyzing these sounds. Research using functional magnetic resonance images (fMRI) and positron emission technology (PET) has shown that certain musical characteristics are related to neural activity in both hemispheres (Abrams et al., 2013; Sarkamo & Soto, 2012). For example, the right temporal lobe, an area of the brain responsible for hearing and memory formation, enables us to distinguish between different timbres, pitches, and melodies; changes in tempo and rhythm, however, seem to activate neural activity in both the right and left hemispheres. Characteristics such as musical key, complexity, and preference activate areas associated with the brainstem, cerebellum, limbic system (e.g., the hippocampus, hypothalamus, and amygdala), thalamus, retrosplenial cortex, anterior cingulate cortex, nucleus accumbens, ventral striatum, caudate nucleus and the ventral tegmental. Tempo triggers neural activity in the brainstem and cerebellum. The presence of lyrics activates areas of the brain associated with speech (Broca's area, Wernicke's area, Brodmann Area 47) and the subcallosal cingulate gyrus, which governs the functions of other cerebral structures such as the brainstem, limbic system, thalamus, and hippocampus.
The activation of various regions in the brain in response to music triggers the secretion of neurochemicals, such as hormones, peptides, cytokines, and neurotransmitters that are responsible for various internal reactions (e.g., increases heart rate) and behavior (e.g., foot tapping, dancing, etc.). Music has been linked to the regulation of norepinephrine and epinephrine, neuropeptides, cytokines related to immune functioning (i.e., interlukein 6), neurochemicals (e.g., serotonin, oxytocin, dopamine; Chandra & Levitin, 2013; Menon & Levitin, 2005; Sutoo & Akiyama; Yehuda, 2011), and steroids (e.g., cortisol, estrogen, testosterone; Gangrade, 2012; Yehuda, 2011). Further, the effect of music on the production and secretion of steroids and their receptor proteins has been found to promote neurogenesis (i.e., neuron growth) and learning (Fukuki & Toyotoshima, 2004). Of particular interest is how music influences dopamine levels. Characteristics such as musical key, complexity, preference, and volume influence the concentration and release of dopamine.
Music frequently elicits a sensation that we often describe as "chills" or a tingling sensation across the skin. This common physiological response to music is an example of arousal. Arousal refers to the degree of physical and psychological activation, and can be induced by emotional events, physical strain, sensory stimulation, the effect of drugs, or any event that causes a physiological response. Such events trigger several physiological manifestations of arousal, such as increased heart rate, higher blood pressure, pupil dilation, and increased skin conductance. These physiological changes are the result of the sympathetic nervous system (SNS). The SNS is a branch of the autonomic nervous system that elicits "fight or flight" responses. The SNS moderates the amount of effort and energy required to perform this task and helps prepare us for action by halting biological functions such as digestion (Kalat, 2010). The SNS activates the sympathetic adrenal medullary axis, which triggers the secretion of norepinephrine and epinephrine. These hormones are responsible for inducing physiological responses such as increase heart rate, increased blood pressure, skin conductance, respiratory rate all indications of arousal. Tempo, volume, dynamic variation, preference, and degree of familiarity all influence arousal levels.
Movies, TV shows, and commercials frequently use music to convey the emotion of a scene or the production as a whole. For example, the "Love Theme" from The Godfather conveys a feeling of melancholy that mirrors the film's plot. Or consider the theme song from Star Wars: its bold opening statement suggests a feeling of hope and optimism that characterizes the message of the film. What triggers these different emotions? Research largely suggests that different musical characteristics can induce different emotional responses. Generally, listening to music in a major key or low complexity music tends to elicit positive emotional feelings, such as happiness, joy, and contentment. On the other hand, listening to music in a minor key or highly complex music can make the listener feel negative emotions, such as fear, anger, and sadness. These emotional feelings can also be influenced by the song's tempo, as we mentioned earlier.
Music can elicit emotions in a number of ways. One is through physiological mechanisms, such as activating areas of the brain that are associated with emotional processing (i.e., the limbic system) or by triggering the release of neurochemicals and steriods (i.e., serotonin, dopamine, cortisol) that regulate emotional responses. Another way is through conditioning effects. Conditioning refers to the repeated pairings between an initially neutral conditioned stimulus and an affectively valenced, unconditioned stimulus. The conditioned stimulus, after the pairing, is then able to conjure the same affective state as the unconditioned stimulus. Music can also influence emotional responses by the degree to which the music either fulfills or violates in-grained expectations regarding its attributes. Within every culture there exist expectations about the perceptual organization of music (i.e., the structure of melody and harmony). Composers follow the tenets of music theory to develop melody and harmony, but even non-musicians hold unconscious psychological expectations about the form and function of a piece of music. These are largely established through schemas and learned associations. Finally, listening to music, especially our favorite music, can trigger the recall of autobiographical memories (i.e., "they're playing our song") and the emotions attached to those memories, as well as feelings of nostalgia.