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Published March 23, 2011 | Supplemental Material + Published
Journal Article Open

Distinctive Features of Saccadic Intrusions and Microsaccades in Progressive Supranuclear Palsy

Abstract

The eyes do not stay perfectly still during attempted fixation; fixational eye movements and saccadic intrusions (SIs) continuously change the position of gaze. The most common type of SI, square-wave jerks (SWJs), consists of saccade pairs that appear purely horizontal on clinical inspection: the first saccade moves the eye away from the fixation target, and after a short interval, the second saccade brings it back toward the target. SWJs are prevalent in certain neurological disorders, including progressive supranuclear palsy (PSP). Here, we developed an objective method to identify SWJs. We found that SWJs are more frequent, larger, and more markedly horizontal in PSP patients than in healthy human subjects. Furthermore, the loss of a vertical component in fixational saccades and SWJs was the eye movement feature that best distinguished PSP patients from controls. We moreover determined that, in PSP patients and controls, the larger the saccade the more likely it was part of a SWJ. Furthermore, saccades produced by PSP patients had equivalent properties whether they were part of a SWJ or not, suggesting that normal fixational saccades (microsaccades) are rare in PSP. We propose that fixational saccades and SIs are generated by the same neural circuit and that, both in PSP patients and in controls, SWJs result from a coupling mechanism that generates a second corrective saccade shortly after a large fixation saccade. Because of brainstem and/or cerebellum impairment, fixational saccades in PSP are abnormally large and thus more likely to trigger a corrective saccade, giving rise to SWJs.

Additional Information

© 2011 The Authors. Received May 17, 2010; revised Jan. 13, 2011; accepted Jan. 20, 2011. This work was supported by the following funding agencies: Barrow Neurological Foundation (S.L.M., S.M.-C.), Arizona Biomedical Research Commission (S.M.-C.), National Science Foundation Awards 0643306 and 0852636 (S.M.-C.), National Institutes of Health Grant EY06717 (R.J.L.), the Office of Research and Development, Medical Research Service, Department of Veterans Affairs (R.J.L.), The Evenor Armington Fund (R.J.L.), and the Oasi Institute for Research and Care (Instituto di Ricovero e Cura a Carattere Scientifico) on Mental Retardation and Brain Aging (Troina, Italy) (A.S.). J.O.-M. is a Fellow of the Pedro Barrié de la Maza Foundation. We thank Isabel Gomez-Caraballo, Manuel Ledo, and Andrew Danielson for technical assistance, and Hector Rieiro for his comments.

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Published - OteroMillan2011p13472J_Neurosci.pdf

Supplemental Material - Movie_S1.mp4

Supplemental Material - Movie_S2.mpg

Supplemental Material - Supplemental_Material.pdf

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August 19, 2023
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