Neuromagnetic beta band abnormalities in stuttering during the perception and production of rhythm

Recent work provides evidence that stuttering can be considered a disorder of timing. A separate body of literature suggests that the neural oscillations within the canonical beta band (12-30Hz) are important for timing and rhythm. The present thesis aimed to link these two areas of research by using magnetoencephalography(MEG) to examine beta band responses to the perception and production of rhythm in adults and children who stutter (AWS and CWS respectively). I first review the neurological substrates associated with normal speech production in order to build a foundation for understanding impaired speech production. Secondly, I review the past ten years of neuroimaging research on developmental stuttering to gain an overall state of the literature and discuss the need to focus research on CWS. Thirdly, I present multimodal neuroimaging evidence for the view that thecore deficit in developmental stuttering is a disorder of timing. Fourthly, I detail the role of the beta band in timing and rhythm as it applies to stuttering. The experimental chapters then follow. The first experiment used MEG in conjunction with dynamic causal modelling (DCM) to measure the effective connectivity between the auditory and motor cortices in the beta band during synchronised and syncopated finger tapping in AWDS. The second experiment aimed to find differences in neuromagnetic beta band activity betweenAWS and AWDS when they are engaged in paced and unpaced finger tapping.The third experiment aimed to assess the feasibility of recording beta band activity from children who do not stutter (CWDS) when listening to trains of rhythmic sounds (390ms, 585ms and 780ms) in order to later assess this in CWS. The fourth and final experiment compared beta band responses of CWS and CWDS while passively listening to either a rhythmic (450ms) or less rhythmic trains of sounds (SOA varying between 300 and 600ms). The results of the first experiment in AWDS showed that both synchronisation and syncopation tapping was driven by auditory feedback in the beta band as evidenced by the winning model containing connections propagating from the auditory to the motor cortex. It also revealed that the difference between synchronisation and syncopated tapping was best explained by connections going from the motor cortex to the auditory cortex and vice versa suggesting that it placed greater demands on motor activity. The second experiment established that AWS exhibit greater betaband modulation compared to AWDS during synchronised but not syncopated fingertapping in the left motor cortex. The third experiment established that CWDS tolerated listening to repetitive trains of sound for a period of about 30 minutes relatively well. It also showed that CWDS exhibit a beta band (12-15Hz) response similar to what has previously been observed in adults. The fourth and final experiment confirmed these results in another sample of CWDS. Interestingly, however, the CWS compared to CWDS in this study showed a beta band response between12-15Hz that was out of phase with the beta band response of CWDS. Overall, Ishow that AWS and CWS exhibit abnormalities in the beta band and build upon the idea that stuttering is related to deficits in timing.