Disrupting the speech motor network: exploring hemispheric specialisation for verbal and manual sequencing using a dual-task approach

<p>Objective: The concept of overlapping neural networks supporting both speech production and fine motor praxis is well accepted; however few studies explore the lateralised behavioural characteristics of language and praxis when performed simultaneously. Method: This study probes the characteristics of the dominant hemisphere by overloading cognitive processing via a novel dual-task paradigm. Two experiments are presented where participants performed sets of motor and speech tasks under single and dual-task conditions. The sets of tasks differed on the extent to which they relied on sequential processing, with the hypothesis that tasks more reliant on this type of processing would suffer a greater performance decrement under dual-task conditions. A reliable measure of hemispheric language dominance was obtained via functional transcranial Doppler (fTCD) ultrasound.Results: Speech production scores in the sequential processing arm were consistently impaired under dual-task conditions, a distinction not seen in the control arm. Results of experiment 2 confirm those of experiment 1, whereby speech scores were most strongly impaired under dual-task conditions and significantly more so in the experimental arm. Motor performance suffered less than speech performance in dual-task conditions over both experimental and control arms in both experimentsConclusion: Data suggest that the common processing capacity for speech and motor praxis can be disrupted through a dual-task paradigm. This novel behavioural data supports theories suggesting a motor-based gestural origin for language and indicates that speech production is more sensitive to the effects of increased processing requirements than are motor tasks</p>