Dysfunction of pontine omnipause neurons causes impaired fixation: Macrosaccadic oscillations with a unilateral pontine lesion
ABSTRACT Macrosaccadic oscillations of eyes (MSO) are regarded as a form of saccadic dysmetria secondary to cerebellar dysfunction. They are usually conjugate, horizontal, and symmetric in both directions of gaze. Using magnetic search coils, we studied a patient with MSO that developed five years following head injury and involved synchronously horizontal, vertical, and torsional planes. The MSO were characterized by directional pre-ponderance and were associated with ipsilateral pontine lesion. We propose a disturbance of fixation mechanisms due to unilateral disinhibition of saccadic burst neurons in three planes. This could arise from either primary or secondary dysfunction of omnipause neurons due to impaired input from the contralateral superior colliculus. The delayed onset is suggestive of denervation supersensitivity as the underlying pathophysiology.
Full-textDOI: · Available from: Klaus Rottach, May 30, 2015
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ABSTRACT: Background: Cavernous malformations consist of dilated vascular spaces separated by fibrous tissues that create a well-defined mass. They are increasingly recognized in the brainstem with the advent of magnetic resonance imaging (MRI). This study was aimed to understand neuro-ophthalmologic findings in the brainstem cavernous malformations. Methods: Fourteen patients with brainstem cavernous malformations, who presented mainly with neuro- ophthalmologic findings, were asked to participate in this stud y. The diagnosis was based on the characteristic MRI findings of well-circumscribed lesions with a mottled core of mixed-signal intensity. All patients received full neuro-ophthalmological evaluation, including oculography in some of them. Results: Seven patients mainly presented with ophthalmoplegia, 3 with abducens palsy, 1 with oculomotor palsy, 1 with gaze-evoked nystagmus, and another 2 with internuclear o phthalmoplegia. In the other 7 patients, the main neuro-ophthalmologic findings were ocular dyskinesia with variable degree of ophthalmoplegia. Six of them had oculopalatal tremor and the other patient showed macrosaccadic oscillation. Six of the 14 patients had a history of recurrent ophthalmoplegia from repeated bleedings of the cavernous malformations. Conclusions: Cavernous malformations in the brainstem can manifest with various ocular motor abnormalities. In patients with recurrent ophthalmoplegia or oculopalatal tremor, cavernous malformation in the brain stem should be considered in the differential diagnosis. J Korean Neurol Assoc 23(2):222-226, 2005
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ABSTRACT: Brain circuits controlling eye movements are widely distributed and complex. The etiology of irrepressible square wave saccades is not fully understood and is likely different for different neuropathologies. In a previous study, spontaneously occurring irrepressible saccades were noted after a cerebrovascular accident that damaged the rostral superior colliculus (SC) and its commissure in a Rhesus monkey. Here, we tracked and quantified the development of similar symptoms in a Rhesus monkey caused by a lesion in the rostromedial SC and its commissure. We documented the changes in these saccadic intrusions while the monkey attempted fixation of a target on three consecutive days post-onset. On the first day, eye jerk amplitude was ~10 degrees and the direction was ~30 degrees above the left horizontal meridian. On the second day, the amplitude decreased to 6.5 degrees and the direction shifted towards vertical, ~20 degrees to the left of the vertical meridian. Size, but not direction, of the eye jerks continued to decrease until intrusions dissipated within one month. Histological examination after ~6 months from the first appearance of the intrusions revealed a lesion in the commissure of the SC. Results from this and the previous study confirm the involvement of the commissure of the SC as the common target for triggering this neuropathy. Our data suggest that commissural fibers play an important role in maintaining normal visual stability. Interrupting the commissure between the two superior colliculi causes saccadic intrusions in the form of irrepressible jerking of the eyes, probably by disrupting inhibitory signals transmitted through the commissure. Furthermore, disappearance of the symptoms suggests that inhibitory fields within the SC are plastic and can expand, possibly via inputs from inter-collicular and nigrotectal pathways.09/2013; 2. DOI:10.12688/f1000research.2-85.v1
American Journal of Ophthalmology 03/2007; 143(3):543. DOI:10.1016/j.ajo.2007.01.007 · 4.02 Impact Factor