Multifaceted Mesodiencephalic Triangles: Insights into Hypertrophic Olivary Degeneration and Oculopalatal Tremor Pathophysiology.

Oculopalatal tremor is a rare neurological disorder characterized by rhythmic oscillations of ocular and palatal muscles. This phenomenon is commonly associated with hypertrophic degeneration of the inferior olive due to loss of GABAergic cerebello-olivary fibers. Oculopalatal tremor highlights the complex interplay between cerebellar, mesodiencephalic, and olivary networks. The principal, medial accessory, and dorsal accessory subnuclei of the inferior olive exhibit rhythmic subthreshold oscillations that are hypothesized to play an important role in oculopalatal tremor. However, delayed tremor onset and variability in hypertrophic olivary degeneration challenge the hypothesis of olivary oscillation as the principal cause of tremorogenesis. A plausible alternative hypothesis is that tremorogenic oscillation emerges from maladaptive cerebellar network plasticity in response to the loss of physiologic climbing fiber activity. The anatomy and physiology of the fastigiobulbar connections are compatible with the clinical characteristics of oculopalatal tremor syndrome, and clinicopathological correlations suggest that the fastigiobulbar pathway is necessary for oculopalatal tremor. Latent brainstem oscillators, released by cerebellar dysfunction, have been proposed but do not explain the anatomical distribution of oscillation. Advanced imaging and computational models have provided insights into possible mechanisms of oscillation but underscore the need for further studies, particularly in a suitable animal model, which does not exist.