Cortical and subcortical mechanisms in persistent stuttering ...

Chapter 1 Introduction
Genetic susceptibility
Stuttering has been long recognized to have a genetic component (Suresh et al., 2006). Family
clustering is frequently reported, several twin studies document a high degree of heritability
and male relatives of female stutterers are at greater risk to develop stuttering; an excellent
overview is given by Yairi and Ambrose (2005). The role of genetic contributions in the
aetiology of stuttering is complex, multifactorial, and heterogeneous (Fisher, 2010). Geneticlinkage
studies yielded suggestive evidence of linkage at multiple chromosomal sites with
little overlap among independent data sets (Kang et al., 2010). One example of suggestive
linkage has its locus on chromosome 12q and was found in a study which included
consanguineous families in Pakistan (Riaz et al., 2005). A continuative analysis of
chromosome 12q23.3 genomic region in consanguineous Pakistani families revealed genetic
abnormalities in the lysosomal enzyme–targeting pathway (Kang et al., 2010).
1.4 Approaches to explain stuttering
The phenomenon of stuttering gave rise to manifold theories, each shaped by the perspective
of a certain field such as for example analytic psychology (Damste et al., 1968), speech and
language pathology e.g. (Bloodstein and Ratner, 2008; Van Riper, 1971; Yairi and Ambrose,
2005), psychology e.g. (Smith and Kelly, 1997; Starkweather and Gottwald, 1990), linguistics
e.g. (Coulter et al., 2009; Howell, 2004; Postma and Kolk, 1993), biomechanics e.g. (Civier et
al., 2010; Namasivayam et al., 2009; Van Lieshout, 2004) and neuroscience e.g. (Alm, 2004;
Brown et al., 2005; Büchel and Sommer, 2004; Kell et al., 2009; Ludlow, 2000). This
multiplicity of approaches is plausible due to the fact that a broad assortment of linguistic,
cognitive, and sensorimotor processes is involved in speech production.
We focus on stuttering as a motor disorder. Before I detail this speech motor control
perspective I briefly mention the psycholinguistic perspective, not only because it has strongly
influenced stuttering research but also because this perspective was considered in the third
study (phoneme identification) included in this dissertation. An awareness of the diverse
approaches to problems in stuttering is important, because a certain experimental result may
be given disparate interpretations by different investigators.
1.4.1 Psycholinguistic approach
It is still a matter of debate, whether stuttering is a language disorder or a motor control
disorder (Kent, 2000). The challenge in understanding stuttering is the distinction between
impairments of the language system and impairments of motor control per se (Kent, 2000).
Several attempts to explain stuttering favor the fluency failure resulting from weakness in
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