Disorders of the basal ganglia and cerebellum: a comprehensive review of speech sensorimotor symptoms and responses to feedback perturbations

Abstract Situated within critical cortical-subcortical sensorimotor circuits, the basal ganglia and cerebellum are thought to play important roles in both feedforward and feedback mechanisms of speech sensorimotor control. Motor speech impairments and speech-related sensory deficits are indeed common in disorders involving these two structures such as Parkinson’s disease, dystonia, and cerebellar degeneration. Recently, several studies have also investigated the impact of these disorders on the feedforward and feedback components of speech sensorimotor control by examining immediate compensation to unexpected auditory perturbations (auditory-motor compensation) and across-trials adaptation to predictable auditory perturbations (auditory-motor adaptation). Additional studies have investigated how the speech of patients with these disorders is affected by pharmacological interventions and deep brain stimulation of neural substrates related to the basal ganglia or cerebellum. This review summarizes and integrates the growing body of literature based on these three lines of inquiry regarding speech sensorimotor control in basal ganglia and cerebellar disorders: (a) motor and sensory impairments, (b) auditory-motor compensation and adaptation, and (c) effects of pharmacological and DBS interventions on symptoms and on auditory-motor compensation/adaptation. The review highlights areas of consistency and inconsistency in the obtained results, demonstrates an apparent dissociation between impact on the phonatory versus articulatory subsystems, and identifies several critical gaps in our knowledge to date. Taken together, these insights call for further studies on speech sensorimotor control in patients with basal ganglia and cerebellar disorders, in particular studies using more rigorous experimental controls as well as innovative neuroimaging and neurostimulation techniques.