Wavelet Analysis of Dual‐<scp>fMRI</scp>‐Hyperscanning Reveals Cooperation and Communication Dependent Effects on Interbrain Neuronal Coherence

Hyperscanning has allowed neuroscience to expand investigations into neuronal activation during social interactions. Rather than analyzing how a single brain responds, we can compare interactions and even synchronization between multiple actors in varying situations. This technique is commonly employed using functional near-infrared spectroscopy (fNIRS). Specifically, social cooperation and competition have been thoroughly investigated using this approach. While functional magnetic resonance imaging (fMRI)-based hyperscanning is becoming more prevalent, a link to this fNIRS-based foundation is missing. We here use a dual-fMRI-hyperscanning setup and an established task to investigate neuronal coherence during social cooperative and competitive tasks. Wavelet transform coherence (WTC) allows us to explore task-specific frequency bands of interest of nonstationary neuronal activation signals of paired participants (n = 60). We show that cooperation, compared to a control task, increases interbrain neuronal coherence in regions associated with social interaction and the theory of mind (ToM) network. Verbal communication prior to the task expands this coherence to different regions of this network, including middle and superior temporal gyrus. This spatial shift suggests additional implementations of the ToM network depending on the cooperation approach taken by the participants. Our findings both support and expand on results by previous fNIRS-based studies and show that WTC is an effective way to model fMRI-based neuronal synchronization, thereby closing the gap between two popular hyperscanning methodologies.