Abstract
Interruption of the dentato-olivary projections, interconnecting the dentate nucleus (DN) and the contralateral inferior olivary nucleus (ION), is predicted to interfere with the DN’ role in estimating direction of gravity. In a patient with pendular nystagmus due to hypertrophy of the ION secondary to predominantly right-sided ponto-mesencephalic hemorrhage, perceived vertical shifted from clockwise to counter-clockwise deviations within 4 months. We hypothesize that synchronized oscillations of ION neurons induce a loss of inhibitory control, leading to hyperactivity of the contralateral DN and, as a result, to perceived vertical roll–tilt to the side of the over-active DN.
Highlights
Hypertrophy of the inferior olivary nucleus (ION) is an interesting phenomenon as it reflects a secondary response to an interruption of afferent connections resulting in increased and abnormally synchronized neuronal activity (Best and Regehr, 2009; Shaikh et al, 2010)
We address the role of the ION and of the dentate nucleus (DN) in the processing of vestibular input and ask whether over-excitation of the DN secondary to disinhibition of the contralateral ION shifts perceived vertical into the opposite direction than previously observed for DN inhibition
While roll under-compensation for left-ear-down positions were unchanged compared to previous recordings, adjustment errors for right-ear-down positions shifted back from roll over-compensation to roll under-compensation. In this case report we describe for the first time a significant shift in the internal estimate of direction of gravity associated with hypertrophy of the ION
Summary
Hypertrophy of the inferior olivary nucleus (ION) is an interesting phenomenon as it reflects a secondary response to an interruption of afferent connections resulting in increased and abnormally synchronized neuronal activity (Best and Regehr, 2009; Shaikh et al, 2010). We report on a patient with hypertrophy of the ION secondary to ponto-mesencephalic hemorrhage and a change in the perception of earth-vertical over time. Following unilateral or asymmetric bilateral lesions along the CVP, this estimate becomes biased as reflected by a tilt in the subjective visual vertical (SVV; Brandt and Dieterich, 1993). In addition to SVV tilts, vestibular tone-imbalances may lead to partial or complete ocular tilt reaction (OTR; consisting of ocular torsion, head roll, skew deviation) depending on the exact topography of the lesion (Brandt, 2000)
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