Scientists at McGill University are trying to understand and quantify what makes music expressive. For example, what specific aspects make one version of a Beethoven sonata convey more emotion?

To decipher the contribution of different musical flavorings, they had Thomas Plaunt, chairman of McGill’s piano department, perform snatches of several Chopin nocturnes on a Disklavier, a piano with sensors under each key recording how long he held each note and how hard he struck each key (a measure of how loud each note sounded).

The pianist’s recording became a blueprint, and the researchers used a computer to calculate the average loudness and length of each note. They created a version using those average values so that the music sounded homogeneous along with other versions.

They found that musicians were more sensitive to changes in volume and timing than non-musicians and that subtle timing differences are critical.

The brain processes musical nuance in many ways, it turns out. Edward W. Large, a music scientist at Florida Atlantic University, scanned the brains of people with and without experience playing music as they listened to two versions of a Chopin étude: one recorded by a pianist, the other stripped down to a literal version of what Chopin wrote, without human-induced variations in timing and dynamics.

During the original performance, brain areas linked to emotion activated much more than with the uninflected version, showing bursts of activity with each deviation in timing or volume.

So did the mirror neuron system, a set of brain regions previously shown to become engaged when a person watches someone doing an activity the observer knows how to do — dancers watching videos of dance, for example. But in Dr. Large’s study, mirror neuron regions flashed even in nonmusicians.