Perverted Downward Corrective Saccades During Horizontal Head Impulses in Chiari Malformation

In response to passive high-acceleration head impulses, patients with low vestibulo-ocular reflex (VOR) gains often produce covert (executed while the head is still moving) corrective saccades in the direction of deficient slow phases. Here we examined 23 patients using passive, and 9 also active, head impulses with acute (< 10 days from onset) unilateral vestibular neuritis and low VOR gains. We found that when corrective saccades are larger than 10°, the slow-phase component of the VOR is inhibited, even though inhibition increases further the time to reacquire the fixation target. We also found that 1) saccades are faster and more accurate if the residual VOR gain is higher, 2) saccades also compensate for the head displacement that occurs during the saccade, and 3) the amplitude-peak velocity relationship of the larger corrective saccades deviates from that of head-fixed saccades of the same size. We propose a mathematical model to account for these findings hypothesizing that covert saccades are driven by a desired gaze position signal based on a prediction of head displacement using vestibular and extravestibular signals, covert saccades are controlled by a gaze feedback loop, and the VOR command is modulated according to predicted saccade amplitude. A central and novel feature of the model is that the brain develops two separate estimates of head rotation, one for generating saccades while the head is moving and the other for generating slow phases. Furthermore, while the model was developed for gaze-stabilizing behavior during passively induced head impulses, it also simulates both active gaze-stabilizing and active gaze-shifting eye movements. NEW & NOTEWORTHY During active or passive head impulses while fixating stationary targets, low vestibulo-ocular gain subjects produce corrective saccades when the head is still moving. The mechanisms driving these covert saccades are poorly understood. We propose a mathematical model showing that the brain develops two separate estimates of head rotation: a lower level one, presumably in the vestibular nuclei, used to generate the slow-phase component of the response, and a higher level one, within a gaze feedback loop, used to drive corrective saccades.

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Enhanced Eye Velocity With Backup Saccades in vHIT Tests of a Menière Disease Patient: A Case Report

Frontiers in Surgery ◽

10.3389/fsurg.2021.727672 ◽

2021 ◽

Vol 8 ◽

Author(s):

Maria Montserrat Soriano-Reixach ◽

Jorge Rey-Martinez ◽

Xabier Altuna ◽

Ian Curthoys

Keyword(s):

Disease Patient ◽

Vestibular Function ◽

Position Error ◽

Head Movements ◽

Slow Phase ◽

Head Impulse ◽

Head Impulses ◽

Eye Velocity ◽

Gaze Position ◽

Horizontal Head

Reduced eye velocity and overt or covert compensatory saccades during horizontal head impulse testing are the signs of reduced vestibular function. However, here we report the unusual case of a patient who had enhanced eye velocity during horizontal head impulses followed by a corrective saccade. We term this saccade a “backup saccade” because it acts to compensate for the gaze position error caused by the enhanced velocity (and enhanced VOR gain) and acts to return gaze directly to the fixation target as shown by eye position records. We distinguish backup saccades from overt or covert compensatory saccades or the anticompensatory quick eye movement (ACQEM) of Heuberger et al. (1) ACQEMs are anticompensatory in that they are in the same direction as head velocity and so, act to take gaze off the target and thus require later compensatory (overt) saccades to return gaze to the target. Neither of these responses were found in this patient. The patient here was diagnosed with unilateral definite Meniere's disease (MD) on the right and had enhanced VOR (gain of 1.17) for rightward head impulses followed by backup saccades. For leftwards head impulses eye velocity and VOR gain were in the normal range (VOR gain of 0.89). As further confirmation, testing with 1.84 Hz horizontal sinusoidal head movements in the visual-vestibular (VVOR) paradigm also showed these backup saccades for rightwards head turns but normal slow phase eye velocity responses without backup saccades for leftwards had turns. This evidence shows that backup saccades can be observed in some MD patients who show enhanced eye velocity responses during vHIT and that these backup saccades act to correct for gaze position error caused by the enhanced eye velocity during the head impulse and so have a compensatory effect on gaze stabilization.

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Recent advances in head impulse test findings in central vestibular disorders

Neurology ◽

10.1212/wnl.0000000000005206 ◽

2018 ◽

Vol 90 (13) ◽

pp. 602-612 ◽

Cited By ~ 26

Author(s):

Jeong-Yoon Choi ◽

Hyo-Jung Kim ◽

Ji-Soo Kim

Keyword(s):

Vestibular Nucleus ◽

Head Rotation ◽

Medial Longitudinal Fasciculus ◽

Head Impulse Test ◽

Vestibular Disorders ◽

Head Impulse ◽

Acute Vestibular Syndrome ◽

Corrective Saccades ◽

Cerebellar Lesions ◽

Horizontal Head

The head impulse test (HIT) is used to evaluate the vestibulo-ocular reflex (VOR) during a high-velocity head rotation. Corrective catch-up saccades that occur during or after the HITs usually indicate peripheral vestibular hypofunction, whereas in acute vestibular syndrome, normal clinical (bedside) HITs should prompt a search for a central lesion. However, recent quantitative studies that evaluated HITs using magnetic search coils or video-based techniques have demonstrated that specific patterns of HIT abnormalities are associated with central vestibular disorders. While normal clinical HITs are typical of central lesions, discrepancies have been observed between clinical and quantitative HITs. The horizontal head impulse VOR gains can be significantly reduced unilaterally or bilaterally (positive HITs) in lesions involving the vestibular nucleus, nucleus prepositus hypoglossi, or flocculus. In diffuse cerebellar lesions, the VOR gain during horizontal head impulses may increase (hyperactive) with corrective saccades directed the opposite way. The presence of cross-coupled vertical corrective saccades during horizontal HITs is also suggestive of diffuse cerebellar lesions. Lesions involving the vestibular nucleus, medial longitudinal fasciculus, and cerebellum may show decreased or increased gains of the VOR during vertical HITs. Defining the differences in patterns observed during abnormal HITs may help practitioners localize the responsible lesions in both central and peripheral vestibulopathy.

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Teaching Video NeuroImages: Macrosaccadic oscillations induced by horizontal head impulses

Neurology ◽

10.1212/wnl.0000000000004291 ◽

2017 ◽

Vol 89 (9) ◽

pp. e116-e116

Author(s):

Seo-Young Choi ◽

You Jin Choi ◽

Jae-Hwan Choi ◽

Kwang-Dong Choi

Keyword(s):

Head Impulses ◽

Teaching Video ◽

Horizontal Head

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Migräne? Arnold-Chiari-Malformation? Oder doch einfach nur eine Migräne?

Praxis ◽

10.1024/1661-8157/a003506 ◽

2020 ◽

Vol 109 (10) ◽

pp. 806-811

Author(s):

Kristian Jäckel ◽

Beat Knechtle

Keyword(s):

Chiari Malformation ◽

Arnold Chiari Malformation

Zusammenfassung. Zusammenfassung: Bei einer jungen Frau mit langjährigen Kopfschmerzen im Sinne einer Migräne ergab eine neurologische Neubeurteilung inklusive neuer Befundung der vorhandenen MRI-Bilder des Schädels die Diagnose einer Chiari-Malformation vom Typ 1. Nach erfolgreicher Operation des Befundes gingen die Kopfschmerzen deutlich zurück. Da aber noch geringe Kopfschmerzen einer anderen Qualität bestehen blieben, ist davon auszugehen, dass eine Migräne sowie als Zufallsbefund die Malformation vorliegen.

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