Friday, April 13, 2012

The Science of Music. Part One: The Ear

Music moves in waves. Those waves flow through the outer ear [E] and crash up against our eardrum forcing the tiniest three bones in our body to move. These bones are located in the middle ear [M] and press against the fluid-filled membrane of the cochlea, which makes up the bulk of the inner ear [I]. As these bones rock to the beat, their vibrations transfer to waves of salty liquid in the cochlea. 

Photo credit:
Cross section of the ear divided into three regions: [E] the outer ear, [M] the middle ear and [I] the inner ear.
Under these waves, hair cells (so named because they look like microscopic bristles) dance back and forth. This minute movement opens ion channels causing certain cells to swell with electric charges. If the cells are bent at a sharp enough angle for long enough they fire an electrical message onward to the brain. Thus, silence is broken and sound has begun.

The cochlea contains 16,000 neurons. In the noisy day-to-day, they are in fact constantly bent since the air is full of vibrations and every one reverberates inside the echo chamber of the ear. But how exactly do we make sense of the musical cacophony that is constantly assaulting these little hairs in our head?

The answer is in the anatomy. Hair cells are arranged like the keys on a piano, with one end tuned to high-frequency sounds while the other only bends to throb of low frequency sounds.

Eventually all of the sounds reach our primary auditory cortex, where neurons are designed to detect specific pitches -- the cortex focuses on finding the notes amidst the noise. We tune out what we can't understand (this is why we can recognize a specific pitch as the same no matter the instrument).

Music is composed in patterns and our brains are designed to love patterns and seek them out. Our desperate neurological search for a pattern is what makes music different from noise. Music is in motion. To us it seems continuos, but in reality each wave is its own unit or piece of the pattern. However, this is not the way we think of music at all, as a wave of separate sounds. We continually construct our own patterns in order to keep pace with the onrush of noise.

Once we find a pattern we begin to make predictions, imagining or possibly hoping for what comes next.  We project imaginary order into the future, transposing the melody we have just heard into the melody we expect to continue hearing. By listening for patterns, by interpreting every note in terms of our personal expectations we turn the scraps of sound into the ebb and flow of a symphony or a song.

To Be Continued:
Next week I'll describe what biologically happens when the patterns and predictions we make are disrupted. The following week I'll get into the biology of the emotional quality of music, primarily its connection with dopamine levels. 

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