Dynamic interhemispheric coordination in face processing

Abstract

Our conscious experience of the world is normally unified. The brain coordinates different processes from the left and right hemispheres into one experience. However, the neural mechanisms underlying interhemispheric coordination remain poorly understood. A mechanistic approach to understanding interhemispheric coordination is \"communication through coherence\" (Fries, 2005; 2015). Using a recently developed time-resolved psychophysics (Fiebelkorn, Saalmann, & Kastner, 2013; Landau & Fries, 2012; Song, Meng, Chen, Zhou, & Luo, 2014), combined with fMRI decoding method, we investigated the interhemispheric coordination through coherence, by focusing on a quintessential case of hemispheric lateralized brain function: face processing in the left and right fusiform face area (FFA). We observed coherent oscillatory fMRI multi-voxel patterns in the left and right FFA when two stimuli presented successively cross visual fields, either initiating coordination from the left hemisphere or right hemisphere. When interhemispheric coordination started from the dominant right hemisphere, a coherent 44{degrees} phase difference between the left and right FFA in 3-4 Hz was observed; whereas when interhemispheric coordination started from the non-dominant left hemisphere, a coherent -17{degrees} phase difference between the left and right FFA in 5.5-6.5 Hz was observed. These results suggest that different phase coherence might mediate the interhemispheric coordination of face perception, depending on whether the initiating hemisphere is dominant or non-dominant. Our findings provide compelling fMRI evidence for interhemispheric coordination through coherence. The time-resolved fMRI decoding approach would be a useful starting point for a more promising approach for future investigation in interhemispheric dynamic coordination with fine-grained spatial and temporal resolution.