Reduction of dopamine in basal ganglia and its effects on syllable sequencing in speech: A computer simulation study

BackgroundReduction of dopamine in basal ganglia is a common cause of Parkinson’s disease (PD). If dopamine-producing cells die in the substantia nigra, as seen in PD, a typical symptom is freezing of articulatory movements during speech production.GoalIt is the goal of this study to simulate syllable sequencing tasks by computer modelling of the cortico-basal ganglia-thalamus-cortical action selection loop using different levels of dopamine in order to investigate the freezing effect in more detail.MethodThis simulation was done using the Neural Engineering Object (Nengo) software tool. In the simulation, two dopamine level parameters (lg and le), representing the effect of D1 and D2 receptors, and therefore the level of dopamine in striatum respectively, can be differentiated and modified.ResultsBy a decrease of the dopamine level parameters lg and le to 50% we replicated a freezing effect after less than 5 syllable productions. Furthermore freezing of action selection in speech was greater for dopamine level reduction in D1 than D2 receptors.ConclusionsIn this study using a neuro-functional brain model, the speech freezing effect results from simulating a reduction of dopamine level in striatum.