The left ventral premotor cortex (PMv) has not been fully acknowledged as a key component of the brain’s network for reading. This region, corresponding to Brodmann area (BA) 6, is cytoarchitecturally distinct from adjacent Broca’s area (BA44/45) and primary motor cortex (BA4) and specifically involved in articulatory codes for speech production. The left PMv is known to receive direct white matter projections from posterior brain regions responsible for visual and phonological processing. Consequently, the region plays a significant role in reading when the expert visual word-form system in the left occipitotemporal cortex is underdeveloped or compromised in early literacy development in childhood or in neurologic disorders in adulthood. Recent functional neuroimaging and brain stimulation studies further suggest that those direct neural pathways connecting the left PMv with the occipital cortex are fully functioning in literate adults, rapidly generating speech motor codes at a very early stage of reading, and faster than thought previously. This region may therefore serve as an alternative and promising cortical target for future neuromodulation research aimed at boosting cognitive components involved in reading.
Kimihiro Nakamura (Fri,) studied this question.