Ventral striatum and stuttering: Robust evidence from a case-control study applying DARTEL.

A prominent theory of developmental stuttering highlights (dys-)function of the basal ganglia (and in particular the ventral striatum) as a main neural mechanism behind this speech disorder. Although the theory is intriguing, studies on gray matter volume differences in the basal ganglia between people who stutter and control persons have reported heterogeneous findings, either showing more or less gray matter volume of the aforementioned brain structure across the brain's hemispheres. Moreover, some studies did not observe any differences at all. From today's perspective several of the earlier studies are rather underpowered and also used less powerful statistical approaches to investigate differences in brain structure between people who stutter and controls. Therefore, the present study contrasted a comparably larger sample of n = 36 people who stutter with n = 34 control persons and applied the state of the art DARTEL algorithm (Diffeomorphic Anatomical Registration Through Exponentiated Lie algebra) to analyze the available brain data. In the present data set stuttering was associated with higher gray matter volume of the right caudate and putamen region of the basal ganglia in patients. Our observation strongly supports a recent finding reporting a larger nucleus accumbens in the right hemisphere in people who stutter when compared to control persons. The present findings are discussed in the context of both compensatory effects of the brain and putative therapeutic effects due to treatment of stuttering.

Impaired motor inhibition in adults who stutter - evidence from speech-free stop-signal reaction time tasks.

Idiopathic stuttering is a fluency disorder characterized by impairments during speech production. Deficits in the motor control circuits of the basal ganglia have been implicated in idiopathic stuttering but it is unclear how these impairments relate to the disorder. Previous work has indicated a possible deficiency in motor inhibition in children who stutter. To extend these findings to adults, we designed two experiments to probe executive motor control in people who stutter using manual reaction time tasks that do not rely on speech production. We used two versions of the stop-signal reaction time task, a measure for inhibitory motor control that has been shown to rely on the basal ganglia circuits. We show increased stop-signal reaction times in two independent samples of adults who stutter compared to age- and sex-matched control groups. Additional measures involved simple reaction time measurements and a task-switching task where no group difference was detected. Results indicate a deficiency in inhibitory motor control in people who stutter in a task that does not rely on overt speech production and cannot be explained by general deficits in executive control or speeded motor execution. This finding establishes the stop-signal reaction time as a possible target for future experimental and neuroimaging studies on fluency disorders and is a further step towards unraveling the contribution of motor control deficits to idiopathic stuttering.

Prenatal testosterone and stuttering.

BACKGROUND: The prevalence of stuttering is much higher in males compared to females. The biological underpinnings of this skewed sex-ratio is poorly understood, but it has often been speculated that sex hormones could play an important role. AIMS: The present study investigated a potential link between prenatal testosterone and stuttering. Here, an indirect indicator of prenatal testosterone levels, the Digit Ratio (2D:4D) of the hand, was used. As numerous studies have shown, hands with more "male" characteristics (putatively representing greater prenatal testosterone levels) are characterized by a longer ring finger compared to the index finger (represented as a lower 2D:4D ratio) in the general population. STUDY DESIGN, SUBJECTS, OUTCOME MEASURES: We searched for differences in the 2D:4D ratios between 38 persons who stutter and 36 persons who do not stutter. In a second step, we investigated potential links between the 2D:4D ratio and the multifaceted symptomatology of stuttering, as measured by the Overall Assessment of the Speaker's Experience of Stuttering (OASES), in a larger sample of 44 adults who stutter. RESULTS: In the first step, no significant differences in the 2D:4D were observed between individuals who stutter and individuals who do not stutter. In the second step, 2D:4D correlated negatively with higher scores of the OASES (representing higher negative experiences due to stuttering), and this effect was more pronounced for female persons who stutter. CONCLUSIONS: The findings indicate for the first time that prenatal testosterone may influence individual differences in psychosocial impact of this speech disorder.

Relationships between personality characteristics of people who stutter and the impact of stuttering on everyday life.

OBJECTIVE: This study investigates the association between the five-factor model of personality measured by the NEO Five-Factor Inventory (NEO-FFI) and the Overall Assessment of the Speaker's Experience of Stuttering (OASES). The OASES measures the adverse impact of stuttering on a person's life. DESIGN: Participants in the present study were 112 persons who stutter from Germany. METHODS: All participants filled in both the NEO-FFI and the OASES questionnaires. RESULTS: Results revealed a strong positive correlation between the personality trait Neuroticism and scores on the OASES. Moreover, Extraversion was negatively correlated with the OASES scores. CONCLUSIONS: The findings suggest that people with higher Neuroticism and lower Extraversion scores experience a greater impact of stuttering on their daily life. The results underscore the importance of considering personality as a potential moderator or mediator factor in future stuttering research and, potentially, also in treatment. EDUCATIONAL OBJECTIVES: The reader will learn (a) about the different personality dimensions reflected by the NEO-FFI, (b) why it is important to consider the impact of stuttering on everyday life from the perspective of the people who stutter and (c) how personality is linked to the Overall Assessment of the Speaker's Experience of Stuttering (OASES).

The role of the DRD2 C957T polymorphism in neuroticism in persons who stutter and healthy controls.

The present study investigates for the first time the influence of the DRD2 C957T polymorphism on personality in persons who stutter. In a recent study, the CC genotype of this single nucleotide polymorphism has been associated with stuttering, which could not be replicated in a follow-up study. Here, we demonstrate, in N=105 persons who stutter, that carriers of the CC and the CT genotype significantly have the highest neuroticism scores. This shows that the inclusion of personality measures in the investigation of the biological underpinnings of stuttering represents an important new avenue. In healthy control persons, a sex by C+/- allele interaction effect could be demonstrated. Female but not male carriers of the C+ variant report the highest neuroticism scores. Because neuroticism has been reported to be associated with stuttering before, the present data support the idea that this personality trait acts as an endophenotype for stuttering, contributing towards bridging the gap from gene variation to the complex pathology. This idea is supported by an additional path model showing that the polymorphism DRD2 C957T influences the self-reported severity of stuttering mainly by its influence on neuroticism (independent of the variable sex).

Investigating personality in stuttering: results of a case control study using the NEO-FFI.

UNLABELLED: A recent study by Iverach et al. (Journal of Communication Disorders, 2010) compared persons who stutter with two normative samples in the context of the five-factor model of personality measured by the NEO Five-Factor Inventory (NEO-FFI). Persons who stutter were characterized by higher Neuroticism, lower Conscientiousness and lower Agreeableness scores in contrast to the normative data from an Australian and a United States sample. Moreover, the authors report that the scores on all five personality dimensions in the stuttering group were within those of the normative samples. A shortcoming of the Iverach et al. study is the lack of a matched control group. In the present study we compared persons who stutter with a control group matched to age and gender. Furthermore, none of the controls had a history of personal and family stuttering. The findings with respect to Neuroticism could be replicated in our sample. But in contrast to Iverach et al. we found higher Conscientiousness and Agreeableness scores in persons who stutter compared to the control group. LEARNING OUTCOMES: The reader of the present study will learn that elevated Neuroticism scores can be observed in persons who stutter across cultures such as Germany or Australia. With respect to other personality dimensions such as Conscientiousness or Agreeableness the picture is much more difficult.