Musicians and their audiences show synchronized patterns of brain activity

Researchers observed "inter-brain coherence" (IBC) — a synchronisation in brain activity — between a musician and the audience.

Photo by chuttersnap on Unsplash
When a musician is playing a piece, and the audience is enjoying it, they can develop physical synchronies. Both might tap their feet, sway their bodies, or clap their hands.

"Through music, the producer and the perceiver connect emotionally and behaviourally," note the authors of a new paper, published in NeuroImage. And now this team, led by Yingying Hou at East China Normal University, has uncovered a connection right down at the neural level. The team has observed "inter-brain coherence" (IBC) — a synchronisation in brain activity — between a musician and the audience. What's more, the strength of this coherence could be used to predict how much the audience enjoyed a piece.

The team used a technique called near-infrared spectroscopy to monitor the brain activity of a professional violinist while he was videoed playing a series of 12 brief, classical pieces. They then used the same technique (which involves shining beams of light through the skull, to monitor changes in blood flow) on 16 women while they watched the video, and listened to all of these pieces. (Because gender differences in inter-brain synchronisation have previously been observed, only women were recruited as listeners.)

The violinist had been instructed to look directly at the camera and maintain a neutral expression while he played the pieces, which each lasted about 100 seconds. If he was enjoying one piece more than another, the team hoped this would not be obvious to the viewers. They were told to gaze at the violinist's face while they listened. After each piece, they rated how much they liked it on a seven-point scale.

The data revealed inter-brain coherence between each of the listeners and the musician, for all of the violin pieces. That is, there were similar patterns of heightened activity in certain key regions of the brain while the violinist played and the other participants listened.

The key regions included the left temporal cortex (which is thought to focus on processing the rhythm of sound information), the right inferior frontal cortex and the postcentral cortices. These two latter regions have been highlighted as important hubs of a hypothesised mirror system that allows a sender and receiver to share brain representations. "In the present study, the frontoparietal mirror neuron system allows audiences to experience or comprehend the mind of the performer as if they were to 'walk in another's shoes'," the researchers believe.

The team also produced an average IBC score for each piece of music, and compared these with the listeners' averaged liking scores for each piece. They found clear correlations. The more popular pieces were marked by stronger inter-brain coherence in the left temporal cortex between the audience as a whole and the performer.

The team also reported that the link between level of coherence and popularity only developed during the second half of each piece. This could be because there are two stages to music appreciation, they suggest. The first stage involves recognising rhythms, and identifying the potential musical structure of a piece. During the next stage, the listener develops aesthetic judgements and experiences emotional resonance, and generates stronger predictions about the sounds that 'should' follow. "If the expectation matches the incoming information, the musical performance will be experienced as pleasant," the team thinks.

More work will be needed to explain why the coherence-liking effect only emerged at a group level, and to explore whether the results obtained here will also apply to other types of musical instrument, and other genres. The team also note that the near-infrared technique only allowed them to look at blood flow in the cortex, not other deeper areas that might be involved in the response to music production and perception, too, such as limbic structures. Also, by design, this study only involved women. Whether men will respond in the same way is unknown.

Still, it's fascinating research. "This study expands our understanding of music appreciation," the researchers write, adding: "The results can potentially be applied to the development of brain indices for predicting public attitudes towards various musical performances."

The averaged inter-brain coherence between the audience and a violinist predicts the popularity of violin performance

Emma Young (@EmmaELYoung) is a staff writer at BPS Research Digest

Reprinted with permission of The British Psychological Society. Read the original article.

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Image source: Vaccaro et al, 2020/Harvard Medical School
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The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.

An unexpected culprit

The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.

What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.

"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.

"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)

fly with thought bubble that says "What? I'm awake!"

Image source: Tomasz Klejdysz/Shutterstock/Big Think

The experiments

The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.

You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.

For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.

Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.

The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.

However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."

The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.

As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.

The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."

The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.

"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.

Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."

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