Abstract
Functional neuroimaging techniques such as PET and functional MRI have been enhanced with a subtraction method allowing us to examine changes in brain activity associated with task performance. An implicit assumption of this method was that the brain is regarded as an input-output system driven by interaction with the external world. However, based on observations of spontaneous brain activity, or activity present even in the absence of task performance or stimuli, brain function can also be conceptualized as an operating-on-its-own system driven intrinsically, with external factors modulating rather than determining the operation of the system. Resting state network analysis with functional MRI is based on this conceptualization. Now this approach is being extended to across-brain network analysis to depict the neural representation of online social interaction. During a dyadic social interaction, two individuals can share visual attention through gaze, directed either to each other (eye contact) or to a third person or an object (joint attention). Eye contact and joint attention are tightly coupled to generate a state of shared attention across individuals. Hyperscanning fMRI in pairs of adults conducting joint attention tasks revealed the existence of an inter-individual neural synchronization in the right inferior frontal gyrus, after all the task-related effects were modeled out. We further conducted a two-day hyperscanning functional magnetic resonance imaging study in which pairs of participants performed a real-time mutual gaze task followed by a joint attention task on the first day, and mutual gaze tasks several days later. The joint attention task enhanced eye-blink synchronization, which is a behavioral index of shared attention. When the same participant pairs underwent mutual gaze without joint attention on the second day, enhanced eye-blink synchronization persisted, and this was positively correlated with inter-individual neural synchronization of the right inferior frontal gyrus. Thus, hyperscanning fMRI showed that the shared attention, a critical element of social interaction, is represented and retained by pair-specific neural synchronization that cannot be reduced to the individual level. The future perspective of this “we-mode” in neuroscience is discussed.
