Objective: To investigate physiology of impaired balance control in Parkinson’s Disease and its modulation by deep brain stimulation

Background: Postural instability leading to falls is the most common cause of morbidity and mortality in Parkinson’s Disease (PD). Vestibular signal is critical for multisensory integration necessary for postural control and maintenance of balance in PD. The cerebellum processes vestibular information and interacts with the basal ganglia network via the subthalamo-ponto-cerebellar and cerebello-thalamic projections. In the present study, volume of tissue activation (VTA) models specific for the deep brain stimulation (DBS) in a given patient were used along with a model of white matter tracts to define physiological underpinnings for impaired balance control.

Method: We have identified individuals with PD and subthalamic nucleus (STN) DBS who had an abnormal false percept of spinning (i.e. vertigo) along the horizontal plane. In these subjects we fused post-DBS surgery imaging with an atlas of deep white matter tracts derived from MR tractography. Using VTA models, we simulated percent of fiber activation in cerebello-thalamic, internal capsule, hyperdirect, medial lemniscus, lenticular fasciculus, ansa lenticularis, and subthalamopallidal tracts.

Results: Perception of self-motion was reproduced when the active DBS location was closest to the dorsal STN. Such modulation consistently activated 90-100% of the cerebello-thalamic tract. In addition the effects of modulation of lenticular fasciculus and ansa lenticularis were variable ranging from null to >90%, as was the activation hyperdirect pathway (~53% to 100%). Note that the ansa lenticularis connects the subthalamus to the brainstem tegmentum, while the hyperdirect pathway directly modulates the subthalamus.

Conclusion: These results reveal that vestibular modulation by STN DBS relies on two mechanisms, one is orthodromic stimulation of cerebello-thalamic fibers; the other mechanism is anterograde modulation of subthalamo-ponto-cerebellar projections (via direct stimulation of the subthalamus or via modulation of ansa lenticularis). While suggesting the involvement of the cerebellum, these results suggest possible DBS targets to modulate balance function in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/modulation-of-cerebellar-and-basal-ganglia-loops-affects-vestibular-processing-in-parkinsons-disease/