Rhythmic cortical dynamics in production of speech and hand motor sequences

Human behaviors, such as speech or object handling, rely on movement sequences. Production of these meaningful movement patterns is supported by concurrent motor and cognitive processes,which presumably involve both local and distributed dynamics in the large-scale cortical networks. This Thesis examined the electrophysiological dynamics underlying sequential motor production in the human cortex. The focus of the Thesis was on rhythmic activity, a signaling feature often associated with neurocognitive processing, and on the question of how rhythmic cortical dynamics link with themotor and cognitive aspects of sequence production and modulate for different types of sequences. Magnetoencephalography (MEG) was used to record cortical population activity during motor performance, while muscle signals were tracked with electromyography (EMG). The first two studies of the Thesis examined the relationship between local rhythmicity in the sensorimotor cortex and speech articulation. The role of the primary sensorimotor region insequence production has remained unresolved. Here, inherent rhythmic activity (~20 Hz) of this region indicated sensitivity for organizing oromotor gestures into sequences (PI). Furthermore, coherent signaling between the sensorimotor cortex and lip muscle was enhanced at the preferredrate (~2–3 Hz) of articulatory production (PII). In the latter two studies, Dynamic Imaging of Coherent Sources (DICS) analysis method wasused to explore interactions between regions when cognitive-motor sequences were produced in object manipulation and handwriting tasks. Coherent rhythmic activity between regions has been viewed as a mechanism for distributed neurocognitive processing. Here, task-sensitive corticocortical (6–20 Hz) coherence was shown to reconfigure to support object manipulation: theleft-lateralized frontoparietal connectivity in simple object handling extended to cover bothhemispheres and temporo-occipital cortices when performance required visuospatial reasoning(PIII). In the context of handwriting, corticocortical phase synchrony highlighted functional elements that were sensitive to variation in complexity and linguistic content of the task: regular handwriting enhanced (~2–5/13–24 Hz) synchrony among central and frontoparietal regions linked with hand coordination and working memory, whereas separate (~7–10 Hz) synchrony within the temporo-occipital system associated with audiovisual language processing emerged specifically to support a kinetically simplified version of the writing task (PIV). In conclusion, the Thesis suggests that the primary sensorimotor cortex functionally reflectssequence-related information in speech production and shows behaviorally optimized coupling with the articulatory muscles. Interregional coherence seems to serve as a mechanism of engaging the task-relevant neurocognitive systems, and phase-coupling further coordinates processing of distinct aspects of cognitive-motor performance.