A Novel Candidate Neuromarker of Central Motor Dysfunction in Childhood Apraxia of Speech

Childhood apraxia of speech (CAS) is conceived as an impairment of the central motor system's ability to program multiple speech movements, resulting in inaccurate transitions between and relative timing across speech sounds. However, the extant neuroimaging evidence base is scant and inconclusive, and the neurophysiological origins of these motor planning problems remain highly underspecified. In the first magnetoencephalography study of this disorder, we measured brain activity from typically developing (TD) children (N = 19, 11 males, 8 females) and children with CAS (N = 7 males) during performance of a speech task designed to interrogate function of the speech areas of the primary sensorimotor cortex. Relative to their TD peers, our sample of children with CAS showed abnormal speech-related responses within the mu-band motor rhythm, and beamformer source reconstruction analyses specify a brain origin of this speech rhythm in the left cerebral hemisphere, within or near pre-Rolandic motor areas crucial for the planning and control of speech and oromotor movements. These results provide a new and specific candidate mechanism for the core praxic features of CAS; point to a novel and robust neurophysiological marker of typical and atypical expressive speech development; and support an emerging neuroscientific consensus which assigns a central role for programming and coordination of speech movements to the motor cortices of the precentral gyrus.