Imaging the Musical Brain
Humans experience pleasure from a variety of stimuli, including food, money, and psychoactive drugs. Such pleasures are largely made possible by a brain chemical called dopamine, which activates what is known as the mesolimbic system — a network of interconnected brain regions that mediate reward. Most often, rewarding stimuli are biologically necessary for survival (such as food), can directly stimulate activity of the mesolimbic system (such as some psychoactive drugs), or are tangible items (such as money). However, humans can experience pleasure from more abstract stimuli, such as art or music, which do not fit into any of these categories. Such stimuli have persisted across countless generations and remain important in daily life today. Interestingly, the experience of pleasure from these abstract stimuli is highly specific to cultural and personal preferences.
Recent brain imaging studies indicate that dopamine-rich areas of the brain become activated when people listen to music or during learning when food and money are presented as rewards. However, these studies cannot exclude the possibility that chemicals other than dopamine contribute to this brain activity. In addition, animal studies indicate that reward can occur in the brain even in the absence of dopamine. The precise role of dopamine in eliciting brain activity that mediates pleasurable experiences has not been well-studied with brain imaging techniques, especially in humans actively engaged in these pleasurable experiences.
A research team headed by Robert J. Zatorre, Ph.D., Professor of Neurology and Neurosurgery at McGill University, used multiple brain imaging techniques — positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) — to study dopamine activity in the brain while people listened to pleasurable music. PET was used to identify brain areas having dopamine activity while fMRI was used to measure blood flow in the brain over time. The researchers hoped to combine the power of PET to identify brain regions showing increased dopamine activity with the power of fMRI to determine the precise timing of these changes while participants listened to pleasurable music.
To investigate, the researchers recruited eight participants having a wide range of musical experience for participation in the study. The participants were aged 19-24 and provided 10 pieces of instrumental music they found pleasurable and to which they experienced chills. The music used in the study included a wide range of genres – classical, folk, jazz, electronica, rock, punk, techno, and tango. For inclusion in the study, the participants must experience chills of similar magnitude at times of extreme pleasure consistently at the same point throughout the music regardless of environment or association with a specific memory. People having a history of medical or psychiatric illness, or substance abuse, were excluded from the study.
During PET scanning, participants listened to self-selected pleasurable music in one session and neutral music in another. In order to utilize similar sets of stimuli throughout the study, as well as for purposes of comparison, one participant’s pleasurable music was used as another’s neutral music. For each PET session, participants listened to music for 15 minutes, were injected with a radiolabeled substance (that competes with dopamine for binding to certain dopamine receptors), and listened to music for another 60 minutes. While listening to music in the PET scanner, participants provided subjective ratings of pleasure by pressing a button when they experienced a chill, and rated both the intensity of each chill and the degree of pleasure felt on a 10-point scale (1 = neutral; 10 = extremely pleasurable). Also during PET scanning, the researchers simultaneously measured a number of other physiological indicators of arousal, including chills, heart rate, respiration (breathing) rate, and skin conductance (electrical impulses on the skin indicative of heightened emotional state).
During subsequent fMRI scanning, participants listened to alternations of their self-selected pleasurable music and other participants’ neutral music over a 40-minute period. Here, participants pressed a button when experiencing a chill and rated the degree of pleasure they experienced while listening to music on a scale of 1 to 3 (1 = Neutral, 2 = Low Pleasure, 3 = High Pleasure).
In a study published in the February 2011 issue of Nature Neuroscience, the research team reports that participants rated their experience of the pleasurable music condition as being more pleasurable than the neutral music condition. Also, the more chills experienced by the participants, the greater the pleasure they reported experiencing while listening to music. In addition, several indicators of physiological arousal, including heart rate, respiration, and skin conductance, increased significantly during the pleasurable music condition as compared to the neutral music condition. Furthermore, the greater the intensity of the chills experienced by participants while listening to music, the greater the degree to which they experienced increases in the aforementioned indicators of physiological arousal.
PET scans showed increased dopamine activity in the striatum (part of the mesolimbic system) during the pleasurable music condition as compared to the neutral music condition. fMRI scans showed that different parts of the striatum released dopamine to ‘want’ or ‘like’ the music at different times. During peak pleasure experiences (as indicated by chills while listening to music), there was increased blood flow in the nucleus accumbens, which may signal liking of the music. By contrast, there was increased blood flow in the caudate during periods of anticipation of peak pleasure experiences (15 seconds before each chill), which may signal wanting (anticipating) the music.
This study provides the first direct evidence that pleasure experienced while listening to music is associated with dopamine activity in the mesolimbic reward system. This phenomenon may be made possible by the ability of music to modulate emotional states and may help to explain why it has remained so highly valued across generations. “These findings provide neurochemical evidence that intense emotional responses to music involve ancient reward circuitry in the brain,” said Dr. Zatorre. “This study paves the way for future work to examine non-tangible rewards that humans consider rewarding for complex reasons,” he said.
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