Dysfunction of pontine omnipause neurons causes impaired fixation: Macrosaccadic oscillations with a unilateral pontine lesion

Department of Neurology, Case Western Reserve University, Cleveland, OH, USA.
Neuro-Ophthalmology (Impact Factor: 0.18). 05/1996; 16(2):99-106. DOI: 10.3109/01658109609009668
Source: PubMed


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.

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    • "In addition to Parkinson’s disease and lesions of the superior colliculus, unilateral lesions of the globus pallidus in Parkinsonian patients 22 and a unilateral lesion of the raphe interpositus nucleus (RIP) 23 have been shown to cause saccadic intrusions. Pallidotomy caused square wave jerks that varied in direction, though in one case the preponderance of eye jerks were directed contraversive to the lesion 22. "
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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.
    Full-text · Article · Sep 2013 · F1000 Research
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    • "Distinct from SWI are MSO, which consist of a series of predominantly horizontal saccades that oscillate the eyes across the point of fixation [9]. Although MSO also show an intersaccadic interval of 200 ms, they often degrade vision because the line of sight does not land on target, but straddles the point of fixation. "
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    ABSTRACT: Fixation instability due to saccadic intrusions is a feature of autosomal recessive spinocerebellar ataxias, and includes square wave intrusions (SWI) and macrosaccadic oscillations (MSO). A recent report suggested that the non-competitive antagonist of NMDA receptors, memantine, could decrease MSO and improve fixation in patients with spinocerebellar ataxia with saccadic intrusions (SCASI). We similarly tested two sisters, respectively of 58 and 60 years, with an unrecognized form of recessive, adult-onset cerebellar ataxia, peripheral neuropathy and slow saccades, who showed prominent SWI and also complained with difficulty in reading. We tested horizontal visually guided saccades (10°-18°) and three minutes of steady fixation in each patient and in thirty healthy controls. Both patients showed a significant reduction of peak and mean velocity compared with control subjects. Large SWI interrupting steady fixation were prominent during steady fixation and especially following visually guided saccades. Eye movements were recorded before and during the treatment with memantine, 20 mg/daily for 6 months. The treatment with memantine reduced both the magnitude and frequency of SWI (the former significantly), but did not modified neurological conditions or saccade parameters. Thus, our report suggests that memantine may have some general suppressive effect on saccadic intrusions, including both SWI and MSO, thereby restoring the capacity of reading and visual attention in these and in other recessive forms of ataxia, including Friedreich's, in which saccadic intrusions are prominent.
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    Full-text · Article · Jan 2005
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