Evidence from the neuroscience of verbal communication shows that when two people share information, their brain activities work in synchrony [1]. Using fNIRS, we analyzed neural activity separately in a speaker and listener and statistically assessed correspondences in their brain activations. We hypothesized that strong brain-to-brain synchronization (B-Bsync) reflects optimal communication (in native English), indicating effortless listening and comprehension while more effortful listening (to accented English) decreases B-Bsync, and B-Bsync ceases completely when the listener fails to understand the speaker. Confirming our hypothesis, certain brain regions were no longer synchronized while processing accented English, suggesting an increased mental effort. [1] Silbert LJ et al. (2014). [2] Peelle JE. (2018).