Lateralization of Brain Activation in Fluent and Non-Fluent Preschool Children: A Magnetoencephalographic Study of Picture-Naming

Abstract

The neural causes of stuttering remain unknown. One explanation comes from neuroimaging studies that have reported abnormal lateralization of activation in the brains of people who stutter. However, these findings are generally based on data from adults with a long history of stuttering, raising the possibility that the observed lateralization anomalies are compensatory rather than causal. The current study investigated lateralization of brain activity in language-related regions of interest in young children soon after the onset of stuttering. We tested 24 preschool-aged children, half of whom had a positive diagnosis of stuttering. All children participated in a picture-naming experiment whilst their brain activity was recorded by magnetoencephalography. Source analysis performed during an epoch prior to speech onset was used to assess lateralized activation in three regions of interest. Activation was significantly lateralized to the left hemisphere in both groups and not different between groups. This study shows for the first time that significant speech preparatory brain activation can be identified in young children during picture-naming and supports the contention that, in stutterers, aberrant lateralization of brain function may be the result of neuroplastic adaptation that occurs as the condition becomes chronic.

Developmental patterns of expressive language hemispheric lateralization in children, adolescents and adults using functional near-infrared spectroscopy

“…At this age range (3-6 years), hemodynamic responses were significantly stronger in the left hemisphere than in the right one, and this left-lateralized language pattern persisted through adulthood. This finding suggests a cerebral specialization of Broca's area in the very early stage of expressive language development, supporting earlier work by Sowman et al (2014) who showed a left cerebral specialization in 3-6 year-old children performing a picture-naming task. In addition, in our study, activity recorded over the posterior control regions (Wernicke's area) did not differ between hemispheres, supporting the hypothesis for a specialization of the left Broca's area for expressive language functions in children and adolescents.…”

“…Others, however, have documented similar language representations in children aged between 7 and 14 years and adults using a verbal fluency task, suggesting that language lateralization patterns related to expressive language are already established by age 7 (Gaillard et al, 2003). Likewise, using a picture naming task in a MEG study, Sowman et al (2014) found significant left lateralization in 24 preschool-aged children aged 3-6 years, suggesting that cerebral regions responsible for language production are already left lateralized at this young age. Moreover, in a recent study by Cai et al (2013), the authors examined a group of left-handed participants with atypical right hemispheric speech dominance and found that they were all also atypically left hemispheric dominant for spatial attention.…”

“…In addition, another major limitation stems from difficulties in assessing expressive language functions in young children, mainly because of movement restrictions and difficulty in assessing task performance during data acquisition. For instance, various neuroimaging techniques, including fMRI (Gaillard et al, 2000;Holland et al, 2001Holland et al, , 2007Szaflarski et al, 2006) and magnetoencephalography (MEG) (Kadis et al, 2011;Ressel et al, 2008;Sowman et al 2014), have been employed to examine the developmental dynamics of expressive language. Alternately, functional near-infrared spectroscopy (fNIRS) is a non-invasive, functional imaging technique that has no major restrictions on movements or verbalization during recording, which renders the technique suitable for investigations in young children (Wilcox et al, 2005).…”

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

“…However, all stuttering groups showed a similar activation across both hemispheres for both conditions. While this result might seem at odds with Sowman et al (2014), it is interesting to note that Sato et al also showed a correlation between increased stuttering severity in adults and reduced lateralisation in the phonemic condition, an effect that was not found in either school-or preschool-aged children.…”

“…Only a few studies have investigated such functions in preschool aged children, and all of these in clinical populations. Sowman, Crain, Harrison, and Johnson (2014) investigated functional activation of brain regions using MEG to a picture naming task in 12 stuttering and 12 typically developing children aged 3-5 years. Their results show a predominant left activation in all children in language regions.…”