What music can mean

17 May 2016

Growing up playing piano and singing in vocal ensembles, Nina So was the student actually intrigued by the theory behind the music. “Music is so fascinating from a biological perspective—how some compositions of different pitch and notes can sound better than others, trigger various kinds of reactions in the brain—and learning that there were scientific answers for these questions naturally drew me to neurobiology,” she says. 

This led to her pursuing an undergraduate degree in biology and music. A neuroscience lesson on early life experience and gene expression levels in the brain first sparked So’s interest in how living organisms operate and express different behaviours. Realising that understanding these behaviours and answering her own questions was to study the brain and molecular fluctuations, she went down the neuroscience path in graduate school to study environmental stimuli, natural acoustic signals, and auditory neuroscience.

The meaning in the music

Broadly, her research interests probe how the brain processes sounds crucial for social communication and extracts information from vocal sounds. All sounds in natural environments are combinations of different frequencies, but harmonic frequencies are very particular, all variations of the “fundamental frequency”. 

Harmonic sounds evoke pitch, which communicates meaning and emotion, and therefore form the basis of most musical systems as well as social cues in language. So’s current project investigates how the brain distinguishes and categorises vocal and pitch-bearing sounds, but particularly on identification of harmonic variables as a distinct category of sound.

Research on these issues frequently use songbird subjects, particularly zebra finches, because of their well-documented social behaviour patterns and dependence on vocal and harmonic cues for courtship, mating, and other basic life functions. 

Since each bird sings a different song, there is a great diversity of sounds with clearly mapped behavioural responses, ideal for identifying neurons for auditory processing and their function, as So does. Zebra finches depend on early life experience in order to sing and be fully socialised, which involves a parental tutoring session lasting about 90 days, starting with a simple version which is modified and practiced for each bird’s characteristic adult song. 

Songbirds’ auditory cortexes have different processing centres, and the process itself is highly hierarchical, so neurons involved in the early stages are less discriminating than neurons that come into play later. Isolating different areas and stages where harmonic identification occurs allows for modifying inquiry and models. This is done by deliberate manipulation or analysis of auditory processing systems where this critical life experience has not occurred to identify the impact of tutoring on processing and selectivity, which shows the plasticity of the auditory system and brain functions which are present regardless of learned behaviour. 

Following neuronal development to social behaviour, So’s team found finches without song experience develop abnormal songs with variable and high pitch, and thus have less of a competitive chance in comparison to normal finches, giving insights into crucial social and acoustic learning needs and brain plasticity. 

Finches’ musical syllables vary along a spectrum of harmonicity, so response is further measured by playing a variety of natural communications signals of different harmonicity, aiding in establishing communicative significance and patterns.

How sound affects us

Though the relationship between music and behaviour has long been of scientific interest, So’s focus on songbirds prompts curiosity. 

“I get that question a lot,” she laughs, “but really, it’s the logical choice for any researcher with a strong interest in music and the determinants of social behaviour; the most fascinating human behaviour involves complex motor and social function, so studying them fully shouldn’t mean we have to stop at human subjects.” 

Many studies on music’s impact on emotion and on the brain use fMRIs, which can only provide a general idea of what happens in the brain, and the timeframe on human subject studies can also be prohibitive. Animal models offer larger diversity as well as the kind of techniques and experiments scientists can perform, including monitoring neurons and single-cell resolutions and manipulating cell function.

The idea of humans as social animals, for whom social interactions are a crucial part of life, remains the underlying theme in So’s corner of neurobiology. Songbirds’ measurable critical period of vocal learning and accessible neurocircuitry give researchers a window in how auditory processes work in human brains in establishing a standard norm and seeing how social behaviour and response varies in alternative scenarios.

For example, in the case of autism, there may be reduced sensitivity to voices and sounds, possibly tied to neuron development or quantity, as well as the possible impact of lack of critical experience on human development. So plans on focusing more deeply on social behaviours to establish how the auditory cortex codes signals, and then compare this to other brain regions to map where auditory neurons send signals. 

“I’m interested to see how auditory information is transformed into behaviour,” she says, “For example, if I hear a particular sound, do I choose to approach or avoid, and how did I learn to make that choice?”

While she hopes to someday move on to applied research on human socialisation, the research prospects afforded by feathery friends are still alluring. There are some big questions that have some interesting clues in the works, she says, including on how the development of neurological systems controlling vocal behaviour relate to the auditory system, and how development hallmarks change in adult stages, and how these hallmarks might be impacted by deprivation of vocal learning environments. 

Recent technological progress in the field allow for researchers to monitor the activity of several neurons together, enhancing current experiments on natural behaviour, learned tasks, and recording of natural activity and neural populations, all in the pursuit of understanding neural development becomes behaviour. 

“It’s a musical mystery, too—what makes one song enough to express a personality and solidify the bonds of a relationship, all without words? For all our talking, we haven’t been able to crack that yet.”

Nina So received her BA in Biology and Music from the University of Virginia, and is currently pursuing a PhD in Neuroscience from Columbia University in New York. She received a Croucher scholarship in 2014.

To view Nina' personal Croucher profile, please click here.