Broca's area responsible for speech production is regulated by lung functions
For more than one and a half centuries, Broca's area, specifically, the pars opercularis and pars triangularis in the left inferior frontal gyrus, has been known to be crucial for human speech production. However, it remains unanswered why this region is recruited for speaking. Speech production involves not only conceptualization and motor planning, but also respiration that provides the airflow necessary for creating sounds. Thus, the role of Broca's area in speech may be shaped by the functionality and the related brain regions associated with lungs. To test this hypothesis, we recruited the patients suffering from chronic obstructive pulmonary disease (COPD) and required them to speak out words while scanning their brains with functional and quantitative magnetic resonance imaging (fMRI and qMRI). We found that the COPD patients exhibited altered cortical responses during speaking in left inferior prefrontal and other regions, and the cortical sites governing breathing functioned abnormally in this task. In addition, using the qMRI to generate longitudinal relaxation time (T1) maps as an index of brain microstructural changes including dendritic maturation and myelination, we discovered that the patients showed significantly higher T1 values than the control group in Broca's area, suggesting reduced myelination and impaired microstructural integrity. Crucially, the data indicated that more severe dyspnea was associated with less well-developed microstructure in Broca's area and its weaker activation. Our study has demonstrated for the first time that lungs may function to shape Broca's area as the speaking center, and this is consistent with the recent work of a lung-brain axis.