The Neuroscience of Silence

“A “Nautilus Magazine” article on the neuroscience of silence titled “This is Your Brain on Silence.”
A popularized review of the scientific research that demonstrates, surprisingly to many, that the brain is actively and positively stimulated by silence as much as by sound. The brain deteriorates as excessive sound or noise assaults the body via blood pressure increases and cellular changes. Further, silence promotes a higher sense of alertness and consciousness. Investigators mentioned ranged from neuroscientists and cardiologists to musicians naturally interested in the neurological role of silence in musical compositions, and tourism marketers seeking to promote Finland’s abundance of silence.”

An extract from “This Is Your Brain on Silence” by Daniel Gross in “Nautilus” Issue 016, August 21, 2014: :
“The word “noise” comes from a Latin root meaning either queasiness or pain. According to the historian Hillel Schwartz, there’s even a Mesopotamian legend in which the gods grow so angry at the clamor of earthly humans that they go on a killing spree. (City-dwellers with loud neighbors may empathize, though hopefully not too closely.)
Dislike of noise has produced some of history’s most eager advocates of silence, as Schwartz explains in his book “Making Noise: From Babel to the Big Bang and Beyond”. In 1859, the British nurse and social reformer Florence Nightingale wrote, “Unnecessary noise is the most cruel absence of care that can be inflicted on sick or well.” Every careless clatter or banal bit of banter, Nightingale argued, can be a source of alarm, distress, and loss of sleep for recovering patients. She even quoted a lecture that identified “sudden noises” as a cause of death among sick children…Surprisingly, recent research supports some of Nightingale’s zealous claims. In the mid 20th century, epidemiologists discovered correlations between high blood pressure and chronic noise sources like highways and airports. Later research seemed to link noise to increased rates of sleep loss, heart disease, and tinnitus. (It’s this line of research that hatched the 1960s-era notion of “noise pollution,” a name that implicitly refashions transitory noises as toxic and long-lasting.)
Studies of human physiology help explain how an invisible phenomenon can have such a pronounced physical effect. Sound waves vibrate the bones of the ear, which transmit movement to the snail-shaped cochlea.
The cochlea converts physical vibrations into electrical signals that the brain receives. The body reacts immediately and powerfully to these signals, even in the middle of deep sleep. Neurophysiological research suggests that noises first activate the amygdalae, clusters of neurons located in the temporal lobes of the brain, associated with memory formation and emotion. The activation prompts an immediate release of stress hormones like cortisol. People who live in consistently loud environments often experience chronically elevated levels of stress hormones.
Just as the whooshing of a hundred individual cars accumulates into an irritating wall of background noise, the physical effects of noise add up. In 2011, the World Health Organization tried to quantify its health burden in Europe. It concluded that the 340 million residents of western Europe—roughly the same population as that of the United States—annually lost a million years of healthy life because of noise. It even argued that 3,000 heart disease deaths were, at their root, the result of excessive noise.
So we like silence for what it doesn’t do—it doesn’t wake, annoy, or kill us—but what does it do? When Florence Nightingale attacked noise as a “cruel absence of care,” she also insisted on the converse: Quiet is a part of care, as essential for patients as medication or sanitation. It’s a strange notion, but one that researchers have begun to bear out as true.
Two-minute silent pauses proved far more relaxing than either “relaxing” music or a longer silence played before the experiment started.
Silence first began to appear in scientific research as a control or baseline, against which scientists compare the effects of noise or music. Researchers have mainly studied it by accident, as physician Luciano Bernardi did in a 2006 study of the physiological effects of music. “We didn’t think about the effect of silence,” he says. “That was not meant to be studied specifically.”
He was in for a quiet surprise. Bernardi observed physiological metrics for two dozen test subjects while they listened to six musical tracks. He found that the impacts of music could be read directly in the bloodstream, via changes in blood pressure, carbon dioxide, and circulation in the brain. (Bernardi and his son are both amateur musicians, and they wanted to explore a shared interest.) “During almost all sorts of music, there was a physiological change compatible with a condition of arousal,” he explains.
This effect made sense, given that active listening requires alertness and attention. But the more striking finding appeared between musical tracks. Bernardi and his colleagues discovered that randomly inserted stretches of silence also had a drastic effect, but in the opposite direction. In fact, two-minute silent pauses proved far more relaxing than either “relaxing” music or a longer silence played before the experiment started.
The blank pauses that Bernardi considered irrelevant, in other words, became the most interesting object of study. Silence seemed to be heightened by contrasts, maybe because it gave test subjects a release from careful attention. “Perhaps the arousal is something that concentrates the mind in one direction, so that when there is nothing more arousing, then you have deeper relaxation,” he says.
In 2006, Bernardi’s paper on the physiological effects of silence was the most-downloaded research in the journal “Heart”. One of his key findings—that silence is heightened by contrasts—is reinforced by neurological research. In 2010, Michael Wehr, who studies sensory processing in the brain at the University of Oregon, observed the brains of mice during short bursts of sound.
The onset of a sound prompts a specialized network of neurons in the auditory cortex to light up. But when sounds continue in a relatively constant manner, the neurons largely stop reacting. “What the neurons really do is signal whenever there’s a change,” Wehr says.
The sudden onset of silence is a type of change too, and this fact led Wehr to a surprise. Before his 2010 study, scientists knew that the brain reacts to the start of silences. (This ability helps us react to dangers, for example, or distinguish words in a sentence.) But Wehr’s research extended those findings by showing that, remarkably, the auditory cortex has a separate network of neurons that fire when silence begins. “When a sound suddenly stops, that’s an event just as surely as when a sound starts.”
Even though we usually think of silences as a lack of input, our brains are structured to recognize them, whenever they represent a sharp break from sounds. So the question is what happens after that moment—when silence continues, and the auditory cortex settles into a state of relative inactivity…
Freedom from noise and goal-directed tasks, it appears, unites the quiet without and within, allowing our conscious workspace to do its thing, to weave ourselves into the world, to discover where we fit in. That’s the power of silence.”

Daniel A. Gross is a freelance journalist and public radio producer who writes about history and science.

See further: Hillel Schwartz “Making Noise: From Babel to the Big Bang and Beyond” [MIT Press, 2011]
Making Noise
“When did the “silent deeps” become cacophonous and galaxies begin to swim in a sea of cosmic noise? Why do we think that noises have colors and that colors can be loud? How loud is too loud, and says who? Attending to sounds at once physical and political, Hillel Schwartz listens across millennia for a trajectory of changes in the Western experience and understanding of noise. From the uproarious junior gods of Babylonian epic to crying infants heard over baby monitors, from doubly-mythic Echo to loudspeaker feedback, “Making Noise” follows “unwanted sound” on its path through terrains domestic and industrial, legal and religious, musical and medical, poetic and scientific. At every stage of this tour de force, crafted in the inimitable prose of one of America’s most innovative cultural historians, Schwartz widens and deepens our sense of the reverberations of soundful lives, urban, suburban, rural, or lost. Never so much a question of the intensity of sounds as of the intensity of relationships, the continual redefinition of noise is a sensitive register of contending generations, classes, and genders.
Drawing upon the archives of children’s authors and anti-noise activists, catalogs of fireworks and dental drills, letters of worried parents and marine biologists, “Making Noise” traces the process by which noise has become as potently metaphorical as the original Babel.”

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