Imagined speech increases the hemodynamic response and functional connectivity of the dorsal motor cortex
Objective . Decoding imagined speech from brain signals could provide a more natural, user-friendly
way for developing the next generation of the brain–computer interface (BCI). With the advantages of
non-invasive, portable, relatively high spatial resolution and insensitivity to motion artifacts,
the functional near-infrared spectroscopy (fNIRS) shows great potential for developing the
non-invasive speech BCI. However, there is a lack of fNIRS evidence in uncovering the neural
mechanism of imagined speech. Our goal is to investigate the specific brain regions and the
corresponding cortico-cortical functional connectivity features during imagined speech with fNIRS.
Approach . fNIRS signals were recorded from 13 subjects’ bilateral motor and prefrontal cortex
during overtly and covertly repeating words. Cortical activation was determined through the mean
oxygen–hemoglobin concentration changes, and functional connectivity was calculated by Pearson’s
correlation coeff...