Exploring the “Music of Silence”

You’ve just attended an exciting concert by your favorite musical group. In the car on the way home and over the next few days, you catch yourself replaying its songs in your head. You “hear” the music in your brain—the melodies, the fast and slow parts, even the dramatic pause before one last refrain of the chorus.

The term for this is “musical imagery”—the voluntary internal hearing of music in the mind without the need for physical action or external stimulation.

Recently, scientists have begun to explore what happens in our brains when we imagine music, and a University of Maryland researcher and colleagues have uncovered something remarkable.

“The music that is produced by your imagination alone is remarkably similar in detail to what is produced in your head when you listen to the actual music,” said electrical and computer engineering Professor Shihab Shamma, who also has an appointment in the Institute for Systems Research.

Two new papers by Shihab and researchers in the Laboratoire des Systèmes Perceptifs at the École Normale Supérieure, PSL University in Paris that explore this “music of silence” were recently published in the Journal of Neuroscience. Postdoctoral researcher Giovanni M. Di Liberto and Ph.D. student Guilhem Marion were Shamma’s co-authors.

For the first paper, the researchers measured the brain activity of 21 professional musicians who both listened to and imagined Bach chorales. They found that neural signals produced by musical imagery can be predicted accurately, similarly to actual listening, and that the signals were clear enough and similar enough to those produced by listening to music that researchers could use electroencephalogram (EEG) results to identify the musical piece being imagined.

While this musical imagination, or expectation, is not limited to trained musicians, their discipline and “internal metronome” make conducting the research more straightforward. “We might need to test 100 non-musicians to equal what we could get from 20 musicians,” Shamma said.

In the second paper, the researchers studied the brain’s ability to learn and detect melodies by predicting upcoming music notes, a process that causes instantaneous neural responses as the music confronts our expectations.

To investigate how the brain reacts to silences during music, Shamma, Di Liberto and Marion again used EEG. They recorded the brain activity of professional musicians as they listened to and imagined Bach melodies and contrasted the brain’s neural signals when the subjects listened to a music stream’s frequent silent pauses with its activity when the subjects were asked to imagine the same melody. This allowed the researchers to investigate neural components the brain generates on its own when listening is not involved.

Similar neural signals emerged in the case of both “listened-to” and imagined notes and silent events, and the researchers found that the internally generated music of silence is in line with the brain’s continuous attempt to predict upcoming plausible notes.

“We’re basically asking, ‘What do silences in music do?’” Shamma said. “Your brain is actually reacting then, and you can record that and study what your brain is producing and predicting without interference from external sounds affecting you.”