No population bias to left-hemisphere language in 4-year-olds with language impairment

Abstract

Background. An apparent paradox in the field of neuropsychology is that people with atypical cerebral lateralization do not appear to suffer any cognitive disadvantage, yet atypical cerebral lateralization is more common in children and adults with developmental language disorders. This study was designed to explore possible reasons for this puzzling pattern of results.Methods. We used functional transcranial Doppler ultrasound (fTCD) to assess cerebral blood flow during language production in 57 four-year-olds, including 15 children who had been late-talkers when first seen at 20 months of age. We categorized cerebral lateralization as left, right or bilateral, and compared proportions with each type of laterality with those seen in a previously tested sample of children aged 6–16 years. We also compared language scores at 4 years for those with typical and atypical lateralization, and then looked at the association the opposite way: comparing those with typical or impaired language in terms of their cerebral lateralization.Results. The distribution of types of cerebral lateralization was similar for 4-year-olds to that seen in older children. Overall, cerebral lateralization was not predictive of language level. However, for children who had language difficulties at 20 months and/or 4 years (N = 21), there was no population bias to left-hemisphere language activation, whereas children without language problems at either age showed a pronounced bias to left-sided language lateralization. Nevertheless, many children with right hemisphere language had no indications of language difficulties, confirming that atypical cerebral asymmetry is not a direct cause of problems.Conclusions. We suggest that atypical lateralization at the individual level is not associated with language impairment. However, lack of lateralization at the population level is a marker of risk for language impairment, which could be due to genetic or non-genetic causes.

Variability in lateralised blood flow response to language is associated with language development in children aged 1–5 years

“…Previous studies comparing typically developed 3-to 5-year-old children to clinical groups suggest left activation in children without language problems. However, findings from this age range also suggest that the reduction or reversal of left-lateralised response to language in clinical groups is not predictive of impairment at an individual level (Bishop et al, 2014). Furthermore, a typical left side activation to phonemic contrasts compared to right side activation to prosodic contrasts (Sato et al, 2011) fits nicely with the proposition by Minagawa-Kawai et al (2011) that newly learned sounds are captured in the left-dominant phonetic and lexical circuits, as opposed to a bilateral activation for syntax, with which prosody heavily interfaces.…”

“…In combination with studies in older and younger samples, as well as clinical populations of a similar age, the results help complete a developmental picture of the lateralised language response and add weight to the growing opinion that such a response develops very early, but is largely guided by experience and other environmental factors. This helps explain why a predominant left activation in typically developing children compared to reduced left activation seen in many clinical populations does not predict language skill at an individual level (Bishop et al, 2014). The results also highlight a novel predictor of ability, namely the variability in lateralised response during this age, previously shown using fMRI data in older adults (Grady & Garrett, 2014).…”

Inconsistent lateralisation of language functions: a risk factor for language impairment?

“…In participants with language impairment, a number of studies have reported a higher incidence of atypical laterality or lower laterality indices when compared to control groups (Whitehouse & Bishop, 2008;Illingworth & Bishop, 2009;de Guibert et al, 2011;Badcock et al, 2012;Waldie et al, 2013;Bishop et al, 2014). This has suggested the possibility that atypical lateralisation could constitute an endophenotype for language impairment, mediating the relationship between an original etiological factor such as a genetic predisposition and impaired language function (Bishop, 2013).…”

Investigation into inconsistent lateralisation of language functions as a potential risk factor for language impairment

“…In the light of such findings, the current paper tests an alternative hypothesis raised by Bishop (Bishop, 2013;Bishop et al, 2014) that consistency rather than degree of language lateralisation may constitute an aetiological risk factor for development of language impairment. Genetic accounts have suggested two underlying phenotypes for cerebral lateralisation: one with a left brain bias and one with no bias to left hemisphere language (Annett, 1985;McManus & Bryden, 1992).…”

“…In participants with language impairment, a number of studies have reported a higher incidence of atypical laterality or lower laterality indices when compared to control groups (Badcock, Bishop, Hardiman, Barry, & Watkins, 2012;Bishop, Holt, Whitehouse, & Groen, 2014;de Guibert et al, 2011;Illingworth & Bishop, 2009;Waldie, Haigh, Badzakova-Trajkov, Buckley, & Kirk, 2013;Whitehouse & Bishop, 2008). This has suggested the possibility that atypical lateralisation could constitute an endophenotype for language impairment, mediating the relationship between an original etiological factor such as a genetic predisposition and impaired language function (Bishop, 2013).…”