Neurocognitive basis of inter-subject variability in speech motor control: Interaction of bottom-up and top-down...

Speech motor control is a complex neuromotor behavior that requires the combined efforts of speech-specific and domain-general brain networks. Over the past decades, multiple studies using the auditory feedback perturbation paradigm or neuropsychological measures have pointed to substantial inter-subject variability in speech motor control. However, the neurocognitive basis underlying such across-subject variability in both normal and disordered speech has rarely been synthesized. In this review, we first analyze the brain structural and functional basis of individualized speech motor control from the perspective of bottom-up auditory-motor processing, emphasizing the importance of neural communication among 'core' regions in the frontal-temporal-parietal and basal ganglia-thalamocortical motor networks. We also discuss the brain temporal and frequency basis of this process, identifying N1-P2 complex and high gamma activity as promising neural markers associated with auditory feedback control, while pre-speech auditory modulation and beta-band oscillations are reflective of feedforward control. Finally, we bring together evidence testing the predictive power of speech-specific and domain-general factors, highlighting that this speech-specific network plausibly interacts with the domain-general network, which exerts top-down modulation on stages of auditory error detection and motor correction. Based on prior findings, we summarize the signal flow in speakers' cortical processing of speech motor control in response to auditory perturbation, providing insights for the neurocognitive basis of inter-subject variability in speech motor control and motor speech disorders.