Cerebral lateralisation of speech production and motor skill
Creators: name: Hodgson, Jessica
Publisher: name: University of Lincoln
Year: 2023
Subjects: C800 - Psychology

description: The association between praxis and language is longstanding in neuropsychology,with evidence revealing that left hemisphere lesions often lead to combined impairmentsin motor control and speech (Rasmussen and Milner, 1975; Goldenberg, 2013). Strongleft hemisphere asymmetry for language is a robust finding at the population level (e.g.Knecht et al 2000a) and similarly the cortical activation patterns of manual praxis forskilled tasks also reveal a left hemisphere bias (Buxbaum et al, 2005; Haaland et al,2004). As such, common neural mechanisms are thought to underlie both speech andmotor skill, especially actions involving fine motor control of the hands. However,evidence for a clear causal relationship between handedness and speech laterality hasproven somewhat weak and inconsistent, due to the wide variation in measurement andclassification approaches used (Groen, et al, 2013). A suggestion by Flowers and Hudson(2013) is that motor and speech laterality are related where they involve a commonfeature of motor output, namely the co-ordination of sequences of movements orutterances to execute a plan or intention so as to achieve a goal; either limb movement orexpression of an idea (e.g. Grimme, et al, 2011). The research conducted here investigatesspeech and motor lateralisation from the hypothesis that sequencing based tasks will bebest able to elicit the predicted left hemisphere activation patterns. Five empiricalchapters are presented detailing a number of studies involving healthy adults, typicallydeveloping children and adults with Developmental Coordination Disorder. The researchuses an emerging technique in cognitive neuropsychology; functional TranscranialDoppler (fTCD) sonography, to explore hemispheric laterality of speech and motor skill.Measurements of the degree of activation in each of the hemispheres during languagetasks, and the use of a skill-based motor task to determine handedness, are the primaryindicators of lateralisation used throughout this thesis. Results from the first 3 chapters 4reveal that 1) atypical patterns of speech laterality are linked to greater performancedifferences on motor skill tasks; 2) that whilst hand preference is established early on inchildhood the relative performance ability between the non-preferred and preferred handsdevelops linearly with age; 3) adults with developmental coordination disorder displayatypical patterns of laterality of speech networks. The final 2 empirical chapters employnovel neuroimaging paradigms to investigate the mechanisms underlying the linksbetween speech and motor sequencing. Results show that the pegboard task elicits lefthemisphere dominant activation regardless of the hand used, unlike other motor taskswith similar properties. Finally a dual task paradigm demonstrates that speech productionsuffers greater impairments than motor skill when performed simultaneously, providingsupport for theories proposing a gestural origin to speech. The data are discussed in termsof the specialisation of the left hemisphere for higher order sequential processing, in thecontext of a lateralised speech-praxis centre model.