The Role of Basal Ganglia and Its Neuronal Connections in the Development of Stuttering: A Review Article

Abstract

Dysfluent speech has the potential to lower one's standard of living drastically. Although there is a lot of theoretical support for basal ganglia dysfunction in developmental stuttering, there isn't any imaging data to back it up. According to several studies, there is a difference in gray matter volume between people who stammer and those who don't. According to studies, the right inferior longitudinal fasciculus and the uncinate fasciculus have higher fractional anisotropy (FA) than fluent controls. A high fractional anisotropy means good white matter integrity in these areas. In children who stutter, grey matter volume was higher in the Rolandic operculum, middle frontal gyrus, superior temporal gyrus, and inferior parietal lobule. These regions are found to be more active in adults who stammer as their speech fluency improves. Stuttering is previously linked to structural deficiencies in the corpus callosum. However, there are differences in the directionality of the findings between studies, which are unknown. According to current theories, stuttering is caused by a breakdown in the integration of auditory data in speech motor planning, which affects behavior tasks that rely on basal ganglia structures. According to some studies, connectivity in the left inferior frontal gyrus (IFG) and basal ganglia of persons with stuttering (PWS) was significantly reduced. Still, it was more robust in the left supplementary motor cortex (SMC) and premotor cortex (PMC) (primary motor cortex). In the Broca's region, there was also decreased perfusion and spectroscopic indicators of neuronal density. Spontaneous speech is more affected by stuttering than conversation, reading, sentence repetition, or singing. As per the dual process theory of language formation, the basal ganglia are essential for formulaic phrases, but the left hemisphere is important for innovative, freshly constructed sentences. According to current theories on their functional traits and connections to cortical areas of control, the basal ganglia are the complex networks in charge of organizing, initiating, carrying out, and controlling motor behaviors. Given the distinct neuroanatomical characteristics of people who stutter, more research into this cohort is required to further our understanding of the illness. The primary goal of this review article is to fill in any knowledge voids between the neuroanatomical structure of the basal ganglia and the onset of stuttering.

Keywords: basal ganglia; dysfluency; gray matter; stuttering; substantia nigra; white matter.