Speech and motor lateralisation in adults with developmental coordination disorder: a functional Transcranial Doppler imaging study

Aim: Research using clinical populations to explore the relationship between hemispheric speech lateralisation and handedness has focussed on individuals with language disorders, such as dyslexia or specific language impairment (SLI). Results from such work reveal 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. This study fills that gap by using an emerging imaging technique in cognitive neuroscience; functional Transcranial Doppler (fTCD) sonography, and an electronic peg moving task, to assess the relationship between speech lateralisation and motor control in participants with Developmental Coordination Disorder (DCD). Method: 12 adult control participants (5 males; aged 18-28 yrs, mean = 20yrs) and 12 adults with DCD and no other developmental/cognitive impairments (4 males; aged 18-43 yrs, mean = 25.3yrs), performed a word generation task whilst undergoing fTCD imaging to establish a hemispheric lateralisation index for speech production. DCD status was confirmed via the Adult Developmental Co-ordination Disorders /Dyspraxia Checklist (ADC) (Kirby, Edwards, Sugden & Rosenblum, 2010). All participants completed a handedness questionnaire, an electronic peg moving task to determine hand skill, a shortened version of the Raven’s Matrices non-verbal reasoning test and the phonological processing section of the York Adult Assessment Battery (YAA-R). Results: As predicted the DCD group showed a significantly reduced left lateralisation pattern for the speech production task compared to controls (mean laterality indices = 1.89 and 3.77 respectively, t(22) = -2.2, p < .05). Results from the Ravens Matrices test were equivalent across groups (t(22) = .008, p = .993) and the groups did not differ significantly on the handedness classification. Performance on the motor skill task showed a clear preference for the dominant hand across both groups (t(23) = -4.472, p < .001), however the DCD group showed significantly slower mean movement times for the non-dominant hand compared to controls (t(22) = 2.270, p < .05). Discussion: This is the first study of its kind to assess hand skill and speech lateralisation in individuals with DCD. The results reveal a reduced leftwards asymmetry for speech and a slower motor performance specific to the non-dominant hand. This fits alongside previous work showing atypical cerebral lateralisation in DCD for other cognitive processes (e.g. executive function and short term memory). The findings are clinically relevant for understanding the profile of handedness in DCD and speak to debates on theories of hemispheric specialisation and language lateralisation