How your brain responds to music

In a cosy room at the Sir C.V. Raman Centre for Physics and Music at Jadavpur University (JU), Shankha Sanyal adjusts a device that looks like a wireless headset with electrodes. It is actually an EEG (electroencephalogram) machine, attached to the scalp of a participant in a study being conducted there. As notes of Hindustani ragas waft in, Sanyal's eyes scan a computer screen displaying images of dancing graphs. The Senior Research Associate at the centre is exploring human cognition through music and fractal mathematics.

His interest in the subject was piqued some 12 years ago during a visit to his alma mater, JU. Sanyal met one of his mentors, Dipak Ghosh, Emeritus Professor of Physics, and in the course of their conversation, Ghosh explained how sounds such as the pitter-patter of rain, birdsong, and the melodies of ragas impacted the human brain. Ghosh emphasised the underlying physics behind this and said scientists now have the tools to understand this effect. Sanyal gave up his job — as a lecturer in an engineering college — and joined Ghosh to explore this correlation at the lab, which the Professor had just established.

After four decades in high-energy physics, Ghosh found himself being increasingly drawn to the field of human cognition, especially the area revolving around people's love for music. He wondered how a particular sequence of notes could evoke sorrow, while another brought joy. "Music is as complex as our brain," Ghosh says. But it also throws light on the state of one's mind.

His team records EEG signals — continuous, random waves generated by the brain in response to music — and analyses them using the mathematical multifractal technique. This method calculates fluctuations, capturing even the smallest of spikes without losing information. "It's like a mathematical microscope into the brain," Sanyal says.

There are five types of brain waves: delta, theta, alpha, beta, and gamma. The human brain generates delta waves when a person is in deep sleep, and theta waves in light sleep. A relaxed brain generates alpha waves. The beta and gamma waves relate to a concentrated and conscious mind. The researchers found that music elevates relaxation, attentiveness, happiness, and stress. They placed multiple electrodes on a volunteer's scalp to capture brain waves from the frontal, parietal, temporal, and occipital lobes and recorded the real-time signals of human cognition.

In a recently published study (bit.ly/mm-eeg), the group showed that music had a greater effect on human emotions than visuals. They experimented with a collection of short video clips from Hollywood films. The participants first saw the videos (with audio and visual content), then watched just the visuals, and finally heard only the audio — which consisted mainly of background music and a bit of conversation. The majority of participants said the audio evoked their emotions the most. The researchers also recorded their brain waves and the corresponding EEG signals supported the participants' feedback. From its research conducted over a decade, the JU group discovered that humans did not undergo any one emotion at a given time; the brain always generates a mix of emotions such as happiness, sadness and stress. That makes cognition a multi-layered field not easy to fathom.

"I think music is one of the most powerful forces we have," says Jonathan H. Burdette, Professor of Radiology at the Wake Forest University School of Medicine, U.S. Burdette studies the effects of music on the human brain using functional Magnetic Resonance Imaging (fMRI). In his lab, researchers performed brain scans on participants as they listened to music from five different genres: classical, country (folk), rock, hip-hop, and Chinese opera. The participants were then asked to select one of their favourite songs during another fMRI session. Following the six scans, the participants rated each piece of music, indicating which they liked the most and which they disliked.

The researchers discovered that when a participant liked a particular piece of music, all four brain lobes synchronised with one another. Conversely, when the music was disliked, the occipital lobe did not communicate with the frontal lobe. "I call it an angry brain," Burdette remarks. The study also found that the fMRI patterns for music that was enjoyed (or disliked) were similar, regardless of the genre. For example, the patterns generated by a rock music fan listening to rock were similar to those produced by country music lovers listening to folk.

Burdette and his collaborators also found a relationship between the hippocampus and the auditory system. The hippocampus is a deep brain structure that controls memory, learning, and emotions. When a person listens to music they like or dislike, the hippocampus becomes active and begins encoding memories. However, when the same person listens to a particularly favourite piece of music of his or her own choosing, the hippocampus remains calm. "In this case, you don't need the memory; that memory is who you are, and it's part of your soul," Burdette says.

Some music immediately triggers old memories. Why it does so is a long-standing mystery of cognition. Hamidreza Namazi, an Adjunct Lecturer at Monash University Malaysia, has found that some music improves memory, and corresponding EEG signals reflect this. Namazi's group discovered a link between human memory and the long-term memory of EEG signals using a mathematical technique called the Hurst exponent. This technique indicates self-similarity in data, meaning the signal retains memory from past values and repeats over time. Mathematicians refer to this as long-range dependency or long-term memory. Namazi's group found that listening to certain music consistently produces similar EEG data, even after a long period.

"We found a correlation between the memory of the music and the memory of the EEG signal," says Namazi. Researchers have yet to explore the effect of rearranging musical structures on human memory. "We expect that changes in the structure of the music could help to improve memory," Namazi adds.

Music is not just sound, but encapsulates silence, too. "The universe is made up of two things: atoms and voids, and so is music," Ghosh says. A musical piece is composed of notes and pauses, or voids. Ghosh says his group drew inspiration from a quote attributed to Mozart: "The music is not in the notes, but in the silence between." In collaboration with ITC Sangeet Research Academy, Kolkata, the researchers studied how the silence between two notes in music affected cognition.

The team selected 36 Hindustani vocal pieces, each two minutes long, sung by eight singers. The pieces were based on four ragas — Bhairav, Darbari Kanada, Miyan ki Malhar, and Todi. Participants listened to the music while the researchers recorded their brain signals. The selected ragas evoked different emotions in the brain, including excitement, happiness, sadness, relaxation, and attentiveness. These emotions, in turn, generated dynamic brain waves, such as the flight of a flock of birds. The researchers counted the number of pauses or voids in the clips and analysed the EEG signals using multifractal techniques.

The study found that as the number of pauses in the music decreased, the complexity of brain activity increased in some regions of the brain, such as the frontal lobe. Conversely, the brain's activity became less complex when there were more pauses. This research opens up new possibilities in understanding how music, including its pauses, affects the brain. "We realised how void can be distributed to create melodious music through this study," says Ghosh.

Colour perception is another mysterious area of cognition. In a study (bit.ly/neu-cog), Souparno Roy and others, also from the JU centre, established a connection between music and colour. Participants chose different colours after listening to various types of music. The more complex the music, the more likely were they to choose red or reddish hues. Conversely, they chose blue or greenish tints when listening to simpler music. "We hope this study will advance research in colour perception," Roy says.

In addition to cognitive studies, such research can have future applications in industries such as neuromarketing, interior design, and music therapy. "I think the study of music and physics is far ahead of its time and holds enormous potential for exploring human cognition," Ghosh remarks.

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High Notes