Cortical and subcortical mechanisms in persistent stuttering ...

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movements which enable a fast detection and correction of articulation. Psycholinguistic aspects of language generation are not considered in the model. Rather it details the production process and the link of production perception interaction. By providing a neuroanatomical framework to understand fluent as well as stuttered (Civier et al., 2010; Max et al., 2004) speech production it is helpful to consider this model for studies on stuttering. More details on the DIVA model are given in Appendix A. 1.2 What is stuttering? Stuttering is an impairment of “Speech that is characterized by frequent repetition or prolongation of sounds or syllables or words, or by frequent hesitations or pauses that disrupt the rhythmic flow of speech. It should be classified as a disorder only if its severity is such as to markedly disturb the fluency”, (“International Classification of Functioning, Disability and Health” ICD-10 F98.5 A; WHO, 2007a). As a consequence of stuttering, the affected individual is disabled in performing daily tasks that rely on spoken communication. This handicaps the individual to maintain a desired occupation or to fulfill economic needs (Yaruss, 2010). The core symptoms of stuttering are dysfluencies. These are features in speech production that can be observed to a different extent in everybody’s speech. The discrimination between typical dysfluencies and stuttering-like dysfluencies requires their qualitative description. Typical or so called other dysfluencies include interjections (“mhm”, “yes”), phrase repetitions (“this is a this is a phrase repetition”), multisyllabic repetitions (“multi multisyllabic”), revisions (“revi repetition”) that are not perceived as stuttering. As to stuttering-like dysfluencies consensus exists regarding part word repetition (p-p-p-partword) and dysrythmic phonation such as unintended audible prolongations of sounds and unintended momentary cessation of phonation/articulation (block) (Yairi and Ambrose, 1992; Yairi and Ambrose, 2005). There is, however, an ongoing debate on whether undue tension or struggle is a criterion to rate a single syllable word repetition (“I-I-I see”) as a stuttering-like dysfluency or not (Bloodstein and Ratner, 2008; Ward, 2006; Yairi and Ambrose, 2005) and whether a cut-off value (e.g. 3 % of stuttered syllables) is necessary to label stuttering (Sandrieser and Schneider, 2008; Ward, 2006). This debate reflects the two opposing views of stuttering as either a quantitative variation along the continuum of normal speech dysfluency (continuity hypothesis; Bloodstein, 1970; van Lieshout et al., 2007) or a qualitatively separate disorder with a distinction between stuttering and normal dysfluency (Johnson, 1959; Yairi and Ambrose, 2005). In the current studies I determined stuttering presence and severity 12
Chapter 1 Introduction according to the German version of the stuttering severity index (Sandrieser and Schneider, 2008) as described in the methods sections of the included studies. 1.3 Subtypes of stuttering Scientific approaches to explain stuttering are diverse and consequently many different attempts to classify the disorder exist. These attempts are clearly influenced by the Zeitgeist in which they emerged. Ehud Yairi wrote an excellent review on these attempts of subtyping stuttering (Yairi, 2007). A reliable and standardized categorization would obviously be of great advantage for scientific studies. A current PubMed search clearly indicates that a separation between acquired [neurogenic] stuttering, psychogenic stuttering, and persistent [developmental, idiopathic] stuttering is commonly used these days (Lundgren et al., 2010). Therefore this etiology-based classification is briefly introduced here. 1.3.1 Acquired stuttering Acquired stuttering occurs in adulthood and is related to aberrant neurogenic conditions including for example cerebrovascular lesions, traumatic brain injuries, seizure disorders and Parkinson’s disease (Lundgren et al., 2010). Various cortical and subcortical lesion sites are related to acquired stuttering (see Appendix B, Table B-1). There is a lot to gain from studies of acquired stuttering, where the causal disruption is more easily identified and the short period between onset and examination helps to assure that observed abnormalities are not secondary but indeed causal. Therefore, a detailed overview on locations of brain injuries that induce speech dysfluencies, criteria for the differential diagnosis, cases of chased stuttering due to brain lesions and current knowledge from deep brain simulation and stuttering is given in Appendix B. 1.3.2 Psychogenic stuttering Psychogenic stuttering occurs in adulthood as a result of psychological trauma (Baumgartner and Duffy, 1997). A reliable differential diagnosis of acquired from psychogenic stuttering, based on perceptual features of speech characteristics, is problematic. It appears that the rapid, favorable response to the treatment serves best to differentiate the psychogenic cases from the neurologic cases (Lundgren et al., 2010). 1.3.3 Persistent stuttering All studies introduced in this dissertation aim at elucidating pathomechanisms in persistent stuttering because it is a frequent disorder with unclear etiology. For that reason I give more details on this disorder. Persistent stuttering occurs in childhood without obvious reason. The 13
Page 1 and 2: Cortical and subcortical mechanisms
Page 3: Statement of Originality I hereby d
Page 6 and 7: Appendix B - Stuttering and acquire
Page 8 and 9: PM premotor cortex PMd dorsolateral
Page 10 and 11: addition I conducted an fMRI study
Page 14 and 15: aforementioned description of the s
Page 16 and 17: encoding lexical, grammatical, phon
Page 18 and 19: 1.5.1 The cerebral dominance hypoth
Page 20 and 21: motor hand area in adults who stutt
Page 22 and 23: Figure 1-1 from Mink, 1996: Schemat
Page 24 and 25: dystonia (Berardelli et al., 2008).
Page 26 and 27: Table 1-2 Results from diffusion te
Page 29: Chapter 2 Original articles 2 Origi
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Chapter 2 Study 2 Excitability of t
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Chapter 2 Study 3 Phoneme Categoriz
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Chapter 4 Conclusions and future pr
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include the conceptualizer, the for
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ω σ´ σ σ st� t� r�� Fi
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Figure A-5 Directions into velociti
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associated with dysarthria, aphasia
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Table B-2 Tuning of fluency by Deep
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A Appendix C Appendix C - Psycholin
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are useful tools to investigate int
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Benabid AL, Pollak P, Louveau A, He
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De Nil LF, Kroll RM, and Houle S. F
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Hickok G and Poeppel D. The cortica
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Levelt WJM. Speaking: from intentio
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Neef N, Paulus W, and Sommer M. Dem
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Smith A and Kelly E. Stuttering: A
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160 unilateral left subthalamic bra
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I thank Tibor Auer for his constant
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