Saccades in Progressive Supranuclear Palsy–Maladapted, Irregular, Curved, and Slow

• Published in: Movement disorders clinical practice (Hoboken, N.J.) Vol. 4; no. 5; pp. 671 - 681
• Main Authors: Shaikh, Aasef G., Factor, Stewart A., Juncos, Jorge L.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.09.2017; John Wiley and Sons Inc
• Subjects: Brain diseases; brainstem; eye movement; Neurons; parkinsonism; superior colliculus; brainstem; parkinsonism; eye movement; superior colliculus
• ISSN: 2330-1619; 2330-1619
• DOI: 10.1002/mdc3.12491

Background Slowed and curved rapid eye movements, saccades, are the well‐known features of progressive supranuclear palsy (PSP). The authors hypothesized that the saccades in PSP not only are slow and curved but also are irregular and have timing deficits. Methods This hypothesis was tested in 12 patients with PSP by measuring vertical and horizontal visually guided saccades using a limbus tracker. Results Both horizontal and vertical saccades were slow and had irregular trajectory and velocity profiles, but deficits were much more robust in vertical saccades. The irregularity in the saccade velocity was due to premature interruptions that either completely stopped the eyes or moved the eyes at much slower velocity along or in the opposite direction of the ongoing saccade. The direction of the eye's trajectory was often changed after the interruption. A conductance‐based, single‐compartment model of the burst neurons embedded in local feedback circuit for saccade generation was simulated. This model mimicked anatomic and physiologic realism while allowing the liberty to selectively change the activation of individual burst neurons or pause neurons. The PSP saccades were comparable to the simulations during reduced activity of the inhibitory and excitatory burst neurons. Conclusion PSP saccades are due to the paucity in burst generation at the excitatory burst neurons and imprecise timing signal from the inhibitory burst neurons. Premature discharge of the inhibitory burst neuron further leads to breaks in the saccade trajectory and maladaptive superior colliculus activity, leading to aberrant saccades that change the intended trajectory of the ongoing saccade.