Lateralisation of speech and handedness in the developing brain

Commonly displayed functional asymmetries such as hand dominance and hemispheric speech lateralisation are well researched in adults. However there is debate about when such functions become lateralised in the typically developing brain. This study examined whether patterns of speech laterality and hand dominance were related and whether they varied with age in typically developing children. 153 children aged 3-10 (M = 5.9yrs, SD = 2.02yrs) performed an electronic peg moving task to determine hand dominance; a subset of 38 of these children also underwent functional Transcranial Doppler (fTCD) imaging during a speech production task to derive a lateralisation index (LI) for hemispheric activation during speech. There was no main effect of age in the speech laterality scores (t (36) = .347, p = .73). Across the whole sample the dominant hand out-performed the non-dominant hand. However, most interestingly, younger children showed a greater difference in performance between their hands (F(1,37) = 7.708 p < .01. Furthermore, this between-hand performance difference significantly interacted with direction of speech laterality, with a smaller difference relating to increased left hemisphere activation (F(1,37) = 7.15 p < .05. This data shows that handedness and speech lateralisation appear relatively determined by age 3, but crucially younger children show a stronger performance preference for their dominant hand, a gap which narrows during development. Results are discussed in terms of the common neural systems underpinning handedness and speech lateralisation.