The Optical Examination of Cortical Activity Associated with Speech-motor Control in Children and Adults who Stutter

Abstract

Adults who stutter (AWS) show robust over-activation of right hemisphere structures during speech production relative to adults who do not stutter (AWNS). This is well documented in the fMRI literature in stuttering. These differences are often interpreted as risk factors for the development of stuttering, however, it remains unclear whether differences in brain activity reflect neural substrates related to the cause of stuttering or plastic changes resulting from a lifetime of stuttering. Few investigations of neural activity underlying speech-motor production in stuttering have distinguished speech motor planning from execution, nevertheless, there is evidence indicating altered planning and execution in AWS relative to AWNS (Chang et al., 2009; Lu et al., 2010). The neural activity of speech motor control in children who stutter (CWS) relative to children who do not stutter (CWNS) is not well documented. Near-Infrared spectroscopy (NIRS) allows the non-invasive acquisition of cortical activity using paradigms that are appropriate for use with children. Using NIRS the cortical activity related to speech motor planning and execution will be examined during two production tasks: a Go/noGo picture identification task and a nonword repetition task in pre-school CWS, school-aged CWS, AWS and age matched peers. The go/noGo task is designed to elucidate speech motor execution. The participants view a picture for 1500ms after which the colour of the picture's border changes to indicate whether or not the child should produce the object's label. This is a covert/overt naming task whereby the participant is unaware whether he will be required to produce speech. The planning of speech motor events is similar across covert and overt conditions. Therefore, by subtracting the cortical activity associated with covert naming from that required for overt naming the remaining cortical activity will be related to execution of speech motor events. The nonword repetition task is designed to elucidate speech motor planning. Participants hear nonwords of various lengths including one syllable (1SYL), three syllables (3SYL) and one syllable nonwords thrice repeated (1SYLx3). Participants are instructed to immediately repeat the nonword. The contrast between the cortical activities generated by 1SYL and 1SYLx3 indexes an increase in motor execution but not motor planning. Whereas the contrast between the cortical activity generated by the SYL3 relative to 1SYLx3 indexes an increase in motor planning but not execution. Comparing the indices of motor planning and motor execution will provide information describing differences in cortical activity that distinguish fluent from stuttering groups. This abstract is developed from ongoing research as part of the first author's dissertation. Results will be presented (at the time of writing we have unanalysed results from three participants).Regarding feedback from the panellists, I am specifically interested in hearing the following:1 – General feedback regarding the paradigm for examining speech motor control.2 – Alternative ways to explore the cortical activity underlying speech motor control.3 – Potential ways to capture the cortical activity for language processing along with indices of speech motor control.4 – The use of NIRS in the acquisition of non-speech motor control data in AWS and CWS.