Abstract

Research using clinical populations to explore the relationship between hemispheric speech lateralisation and handedness has focused on individuals with speech and language disorders, such as dyslexia or specific language impairment (SLI). Such work reveals atypical patterns of cerebral lateralisation and handedness in these groups compared to controls. There are few studies that examine this relationship in people with motor coordination impairments but without speech or reading deficits, which is a surprising omission given the prevalence of theories suggesting a common neural network underlying both functions. We use an emerging imaging technique in cognitive neuroscience; functional Transcranial Doppler (fTCD) ultrasound, to assess whether individuals with Developmental Coordination Disorder (DCD) display reduced left hemisphere lateralisation for speech production compared to control participants. Twelve adult control participants and 12 adults with DCD, but no other developmental/cognitive impairments, performed a word generation task whilst undergoing fTCD imaging to establish a hemispheric lateralisation index for speech production. All participants also completed an electronic peg moving task to determine hand skill. As predicted the DCD group showed a significantly reduced left lateralisation pattern for the speech production task compared to controls. Performance on the motor skill task showed a clear preference for the dominant hand across both groups; however the DCD group mean movement times were significantly higher for the non-dominant hand. This is the first study of its kind to assess hand skill and speech lateralisation in DCD. The results reveal a reduced leftwards asymmetry for speech and a slower motor performance. This fits alongside previous work showing atypical cerebral lateralisation in DCD for other cognitive processes (e.g. executive function and short term memory) and thus speaks to debates on theories of the links between motor control and language production.