JCPSLP vol 14 no 3 2012

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JCPSLP Volume 14, Number 3 2012 155
Libby Smith
(a bundle of nerve fibres that carries messages from one
part of the brain to another) in the left hemisphere differs in
people who stutter compared to fluent speakers (Chang,
Erickson, Ambrose, Hasegawa-Johnson, & Ludlow, 2008;
Cykowski et al., 2010; Sommer et al., 2002; Watkins et al.,
2008). Researchers are not yet sure what causes tracts to
differ in these images, but it may be due to abnormalities
in the protective sheath (myelin) that helps nerve fibres
carry messages (Cykowski et al., 2010). This leads to the
intriguing conclusion that stuttering might be caused by
a problem with the formation of the myelin sheath during
brain development (myelogenesis) (Cykowski et al., 2010).
Unlike much of the brain that develops before birth, the
particular fibre tract implicated in these studies undergoes
myelination during the first two years of life (Yakovlev
& Lecours, 1967). It connects brain areas important
for speech which integrate auditory and speech motor
information (Cykowski et al., 2010). Impaired myelination
would interrupt the normal functioning of this connection.
Despite stuttering being a developmental disorder,
neuroimaging research has so far predominantly involved
adults who stutter and they participate many years after
stuttering onset. There remains a possibility that the brain
differences reported in neuroimaging studies involving
adults may be a consequence of stuttering behaviour of
the individuals over time, rather than a result of abnormal
development in the early post-natal period. By including
Neuroimaging studies conducted over the last
decade have consistently found differences in
brain anatomy and brain activation patterns during
speech between people who stutter and fluent speakers
(Beal, Gracco, Lafaille, & De Nil, 2007; Cykowski, Fox,
Ingham, Ingham, & Robin, 2010; Foundas, Bollich, Corey,
Hurley, & Heilman, 2001; Fox et al., 1996; Neumann et
al., 2003; Sommer, Koch, Paulus, Weiller, & Buchel, 2002;
Watkins, Smith, Davis, & Howell, 2008). It is likely that a
complex interaction of genetic and environmental factors
influence the development of brain structure and function in
children who stutter, altering the normal functioning motor
speech networks in the brain (Watkins, Gadian, & Vargha-
Khadem, 1999).
Brain activation studies (using positron emission
tomography [PET] or functional magnetic resonance
imaging [MRI]) reveal that people who stutter use the
speech motor areas in the left side of their brain less than
fluent speakers and use their right side more than fluent
speakers (Brown, Ingham, Ingham, Laird, & Fox, 2005;
Watkins et al., 2008). These findings suggest that people
who stutter may use a compensatory network for speech
due to inadequate function in the normal speech areas
in the left hemisphere of the brain (Preibisch et al., 2003;
Sommer et al., 2002).
Recent research using diffusion tensor imaging (a type
of MRI) has found that a particular white matter fibre tract
Developmental stuttering
A paediatric neuroimaging study
Libby Smith
Research update
Libby and a research participant prepare for a magnetic resonance imaging (MRI) scan