From the perspective of neuroscience, listening to music is one of the most complex things you can do. Many parts of your brain have to work together to comprehend even the simplest tune. So what is music really doing to our minds?
The Mechanics of Music
There isn't a single music center of the brain, in large part because listening to even very simple music combines a bunch of distinct neurological processes. Let's first look at the more strictly mechanical aspects of listening to music. As you might be able to guess from its name, the auditory cortex is an important part of processing the sound of music. Part of the temporal lobe, the auditory cortex takes in information from the ear and assesses the pitch and volume of the sound.
Other parts of the brain deal with different aspects of music. Rhythm, for instance, is only connected in a relatively minor way to the auditory cortex. A lot goes into keeping even relatively simple, regular beats - tapping along to something as basic as a 1:2 rhythm brings in the left frontal cortex, left parietal cortex, and right cerebellum, and more unusual rhythms bring in still more areas of the cerebral cortex and cerebellum.
Tonality - the building of musical structure around a central chord - is another crucial part of musical understanding, and it reels in still more parts of the brain. The prefrontal cortex, cerebellum, and many parts of the temporal lobe all go into our ability to recognize the tone of a given piece of music. Taken all together, this means that music already brings in three out of four of the lobes of the human brain - frontal, parietal, and temporal, with only the visual processing occipital lobe unaffected...and there might be a bit more to say about that in a moment.
Music is sometimes given a quick and dirty classification as a "right-brained" activity, meaning that the act of processing music is centered on the right hemisphere of the brain. While this fits nicely with the general dichotomy that the left side of the brain is more engaged in logic and the right in creativity, these are all pretty big oversimplifications. While it is broadly true that music involves more of the right hemisphere than the left, the fact is that the processing of music is so diffuse and decentralized throughout the brain that it's hard to come up with any single category for all the different areas involved.
The Deeper Impact
Those, however, are just the basic mechanical aspects of listening to music. A good song can trigger a cascade of secondary responses, often involuntarily. An obvious example of this is the propensity to move in time with music - not so much dancing, which is an active, independent process, but simple motions like tapping one's toe along with the song. This is caused by stimulation of neurons in the motor cortex.
Another intriguing side-effect of listening to music is the activation of the visual cortex, found in the back of the brain in the occipital lobe. Research indicates that some music can provoke a response in this part of the brain, as the engaged listener tries to conjure up appropriate imagery to match the changes and progression in the music.
Part of the reason that music tends to be so meaningful to us is that it's deeply intertwined with memory. Because the brain is so completely engaged in listening to music, it's one of the parts of a situation that is remembered most clearly later on. Songs and pieces of music can serve as powerful triggers for memories - hence the cliche about couples and "their song."
And let's not forget the language aspect of music. Obviously, not all songs have lyrics, but those that do draw upon the language centers of the brain. The two main parts of the brain associated with language are Wernicke's area and Broca's area, the former of which is found in the temporal lobe while the latter is in the frontal lobe. Previous research has tended to indicate that Wernicke's area is more crucial to language comprehension, while Broca's area is more tied up in language production, though it now appears that there's significant overlap. In any event, we can add them to the list of brain regions tied up in music comprehension.
The Subjective Sounds
So just why does music carry so much meaning for us? Because music draws on so many different parts of the brain, it's hard to say with certainty, but that might actually help give us an answer. Music is extraordinarily complex even before it enters the brain - the pitch of music, for instance, has to be much more stable than frequencies we normally sound, or else it would just devolve into chaotic noise. The same is true of rhythm, tone, and other musical properties - these have to be highly complex to cohere into anything even vaguely musical in the first place.
And it's not as though there's any real objective measure of what counts as "musical" and what doesn't. That shouldn't come as any surprise to anyone who's ever read a music review, but it's crucial to remember just how much the brain is involved as an active participant in shaping our interaction with music. Memory is one of the most obvious influences here - you're more inclined to like a particular piece of music if it carries positive associations, for instance.
It's also possible that a person's particular brain chemistry can affect his or her appreciation of music. Considering how many different parts of the brain are activated by listening to music, even one unusual link in that chain can drastically alter the person's response. There's also plenty of more everyday factors to consider - how much a person knows about music, whether they themselves play an instrument, whether the music has lyrics, and even whether it's a recording or a live performance can all dramatically change the particular neural response to the same basic piece of music.
The Hardwired Responses
If there's one constant in all this, it's that songs carry a tremendous ability to provoke emotional responses - indeed, it can even seem that that's our brain's primary concern when it comes to music. Brain imaging studies have shown that "happy" music stimulates the reward centers of the brain, causing the production of the chemical dopamine. That's the same chemical produced from eating great food, having sex, and taking drugs.
Even better, the brain hangs onto the ability to understand the emotional impact of music, even if the finer points of comprehension are lost. One study, for instance, focused on a woman with damage to her temporal lobe - and, by extension, her auditory cortex - that made it impossible for her to comprehend different melodies and other basic parts of musical structure. Even so, she was still able to read the basic emotional content of the music, respond appropriately to "happy" and "sad" music in turn.
This process seems to start early, too. Researchers at Brigham Young University found evidence that infants as young as five months are able to discern when a happy song is playing, and by nine months they've added comprehension of sad music to their repertoire. Interviewed in 2008, BYU music professor Susan Kenney explained what the babies were responding to:
"The happy songs were all in major keys with fairly short phrases or motives that repeated. The tempo and melodic rhythms were faster than any of the sad selections, and the melodies had a general upward direction. Four of the sad songs were in minor keys and all had a slower beat and long melodic rhythms. For an infant to notice those differences is fascinating."
And the effects of such music only increases as we get older. (Considering the babies' responses to the music involved turning their heads slightly, you'd sort of hope it would.) We actually can have physiological reactions to music - happy music with a fast tempo and major key can make us breathe faster, while sad music in a slow tempo and minor key can slow down our pulse and cause blood pressure to rise.
Of course, the roots of those reactions are found back in the brain. It's just another indication of how powerful and multi-faceted our relationship with music really is, and how it's able to change our brains in ways both obvious and so subtle that we can barely comprehend what's happening.
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