Starting at the Ear. The Neuroscience of Music

Music is a universal human experi-ence woven into the fabric of our everyday lives. From a physical standpoint, music is simply structured sound, yet it has the incredible capacity to elicit emotions, shape movement, and foster social connection. The neurobiological explanation for the power of music in the human experience is currently a mystery, and solving this mystery has increasingly gained scientific interest in the last decades. Many approaches have been made by researchers, from neuroimaging and psychological methods in humans, to musicological, evolutionary, and computational modeling approaches. My approach has been simple, grounded in my intuition as a musician and my training as an auditory neuroscientist: our body’s experience of sound begins at the ear, and therefore this is where our investigation must begin.

The ear is the first major point of contact between sound and our nervous system. Structures inside the ear convert mechanical pressure waves in the air (a.k.a. sound) into electrical currents that are transmitted by the auditory nerve to structures in the brainstem, midbrain, and finally the cerebral cortex. The auditory system is incredibly complex, and a lot of processing occurs in brainstem and midbrain structures long before information reaches the huge wrinkly-looking part we typically imagine when we think of the brain. For example, sub-cortical processing is sufficient to inform us where a sound is coming from by computing the microsecond differences between sound reaching our left and right ears. This tells us two things that are relevant to our discussion of music: that many basic functions important for survival happen in very fast subcortical circuits that do not require cortical processing, and because these functions are so important for survival, they are likely conserved across mammalian species.

What does this have to do with music? It turns out that being able to detect sound patterns is essential for survival. If we consider what the sources of rhythmic sounds in the environment are, we will realize that they almost always come from other living beings: footsteps, wingbeats, vocalizations. Any animal needs to be able to detect these rhythms quickly out of background noise in order to recognize and respond appropriately to the presence of a predator, for example, or a prey. The auditory system is therefore always searching for patterns in the constant stream of sound hitting the ears. And what is music if not rhythmic patterns of sound? 

To explore how the auditory system detects rhythmic patterns, I recorded from neurons in the auditory midbrain and auditory cortex of rodents (remembering that these structures are largely conserved across mammalian species). We discovered that even when the nervous system is passively responding to music under anesthesia, neural activity is encoding higher-level patterns that correspond to how we might interpret the musical beat. This does not mean that sleeping rats are perceiving musical beat. It is actually the other way around—the way that neurons respond in the auditory system constrains how we eventually feel the beat in music. 

So, if the mammalian auditory system is organized and optimized for pattern detection, then could it mean that rats or other mammals could perceive musical rythm too? While it is simple to ask a human, the only way we can ask animals what they perceive is by observing their behavior. The way humans express our perception of musical rythm is through movement. Dancing, tapping, nodding, or otherwise synchronizing movements to music is something we do spontaneously, while it is extremely rare to see even our companion animals do this.

However, in another series of studies we discovered that with the appropriate training, even nonhuman animals can be trained to move to explicit metronome beats, and even to subjective musical rythms. Their movements do not exactly match those of humans, but by carefully observing their behavior we can understand that they truly are perceiving a musical rythm. These findings make groundbreaking progress towards unraveling the mystery behind the neurobiological and evolutionary origins of musicality but also raises many new questions. For example, if other mammals are capable of moving to music, why don’t we ever see them doing it? 

THESE FINDINGS MAKE PROGRESS TOWARDS UNRAVELING THE MYSTERY BEHIND THE NEUROBIOLOGICAL AND EVOLUTIONARY ORIGINS OF MUSICALITY

Ongoing projects in my research group explore this and other questions related to neuroplasticity, or the brain’s remarkable ability to connect general abilities together to form new skills even in adulthood through association with reward. Auditory-motor and reward circuits are specifically afflicted in Parkinson’s disease, and we are currently exploring the neural basis for the efficacy of Rhythmic Auditory Stimulation, a commonly used clinical therapy where a patient’s motor symptoms improve profoundly and almost immediately in the presence of rhythmic sounds such as music. Understanding how and why auditory stimulation relieves motor symptoms in this debilitating disease could help us develop improved therapies and treatments.

In a second project, we are gathering longitudinal data on the brain and behavior over one year of intensive musical training in adults aged 40-75 who are learning to play the guitar for the first time. Here, our hypothesis is that the neuroplasticity induced by intensive auditory-motor training—not unlike the process we used to train animals to move to music in previous studies—induces changes to brain structure, function, cognitive ability, and may even delay the natural cognitive decline that occurs with an aging brain.

Finally, regarding why we don’t see our pets moving to music, we believe that in humans, the auditory and motor systems are naturally linked together through reward whereas in other mammals this link is established through training. Therefore, the magic and mystery of music may be a reflection of the characteristics of our nervous system, and thanks to research in the neuroscience of music, we can both enjoy the pleasure of music while using its power as a tool to improve human health.

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