Abstract
One form of communication that is common in all cultures is people singing together. Singing together reflects an index of cognitive synchronization and cooperation of human brains. Little is known about the neural synchronization mechanism, however. Here, we examined how two brains make one synchronized behavior using cooperated singing/humming between two people and hyperscanning, a new brain scanning technique. Hyperscanning allowed us to observe dynamic cooperation between interacting participants. We used functional near-infrared spectroscopy (fNIRS) to simultaneously record the brain activity of two people while they cooperatively sang or hummed a song in face-to-face (FtF) or face-to-wall (FtW) conditions. By calculating the inter-brain wavelet transform coherence between two interacting brains, we found a significant increase in the neural synchronization of the left inferior frontal cortex (IFC) for cooperative singing or humming regardless of FtF or FtW compared with singing or humming alone. On the other hand, the right IFC showed an increase in neural synchronization for humming only, possibly due to more dependence on musical processing.
Highlights
People’s daily life experiences testify to the fact that through cooperation with others we can achieve goals that we could not reach otherwise
wavelet transform coherence (WTC) between participants is meaningful if the continuous wavelet transform (CWT) of each participant does not show change between the rest and task intervals, our data shown in Figure 3 tended change a little at 4 s because the respiration changes CWT at 4 s
We employed a single functional near-infrared spectroscopy (fNIRS) machine to measure the neural synchronization of two participants simultaneously while they were singing or humming together
Summary
People’s daily life experiences testify to the fact that through cooperation with others we can achieve goals that we could not reach otherwise. Studies seeking to identify the responsible brain mechanisms for cooperation have been unable to reveal details about the synchronization of the neural activations (Frith and Frith, 1999). Synchronization during social interactions has been reported using different neuroimaging techniques. Singing together is a form of cooperation seen in all cultures and makes a suitable model to study the neural mechanisms of synchronization (Mithen, 2005). The vocalizations of monkeys often have a synchronized musical nature to them. This property is heard most dramatically in the rhythmic chattering of gelades, which are close cousins of baboon, and the “duet” singing of paired gibbons (Geissmann, 2002). The neural synchronization of cooperative singing may have evolutionarily adapted to make a bond of affection in order to strongly bind groups of people (Dunber, 2010)
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