When people make music together their brain activity synchronizes - even when they aren't playing the same notes.
Scientists from the Max Planck Institute for Human Development in Berlin used electrodes to trace the brain waves of guitarists playing in duets. And, they found, similarities in brain activity couldn't be put down to perceiving the same stimuli or performing the same movements.
Instead, the two brains appeared to be synchronizing to support the coordination of their actions.
The psychologists placed 32 experienced guitarists in pairs and attached 64 electrodes to each of their heads. The musicians were then asked to play a rondo sequence from the Sonata in G major by Christian Gottlieb Scheidler a total of 60 times.
Importantly, the two partners were given slightly different tasks. They had to play in two voices, and one of the two was assigned a leading role, making sure that they both started at the same time and kept the same tempo.
And they found that the difference between leader and follower was reflected in the electrical activity captured by the electrodes.
"In the player taking the lead, synchronization of brain waves measured at a single electrode was stronger, and already present before to the duet started to play," says Johanna Sänger.
This was particularly true for delta waves, which are located in the frequency range below four Hertz.
"This could be a reflection of the leading player's decision to begin playing," Sänger suggests.
The scientists also analysed the correlation between the signals from the different electrodes - and found what they decribe as 'remarkable' results. When the musicians had to actively coordinate their playing, especially at the beginning of a sequence, the signals from the frontal and central electrodes were clearly associated between the two heads.
"When people coordinate actions with one another, small networks within the brain and, remarkably, between the brains are formed, especially when the activities need to be precisely aligned in time, for example at the joint play onset of a piece," says Sänger.
"We assume that different people's brain waves also synchronise when people mutually coordinate their actions in other ways, such as during sport, or when they communicate with one another."