Objective: Skilled motor praxis and speech production display marked asymmetries at the individual and the population level, favouring the right hand and the left hemisphere respectively. Theories suggesting a common processing mechanism between praxis and speech are supported by evidence that shared neural architecture underlies both functions. Despite advances in understanding the neurobiology of this left-hemisphere specialisation the cortical networks linking these two functions are rarely investigated on a behavioural level.
Method: This study deploys functional Transcranial Doppler (fTCD) ultrasound to directly measure hemispheric activation during skilled manual praxis tasks shown to be correlated to hemispheric speech lateralisation indices. In a new paradigm we test the hypothesis that praxis tasks are highly dependent on the left hemisphere's capacity for processing sequential information will be better correlated with direction and strength of hemispheric speech lateralisation
Results: Across two experiments we firstly show that only certain praxis tasks (pegboard and coin-rotation) correlated with direct measurements of speech lateralisation despite shared properties across all tasks tested. Secondly, through novel imaging of hemispheric activation during praxis, results showed that the pegboard differed in the lateralisation pattern created and furthermore that it was significantly related to speech laterality indices, which was not the case for either of the other two tasks.
Conclusion: These results are discussed in terms of a lateralised speech-praxis control mechanism and demonstrates that measurements of motor paradigms through the use of fTCD are reliable enough to provide a new insight to the behavioural relationship been speech and handedness
