Address for correspondence: Prof. Dr. U. Büttner, Neurologische Klinik, Marchioninistr. 15, D-81377 Munich, Germany. Voice: 49 089-7095-2560; fax: 49 089-7095-5561.
ubuettner{at}brain.nefo.med.uni-muenchen.de
Ann. N.Y. Acad. Sci. 956: 99-110 (2002).
The midbrain contains several structures important for the generation
of torsional and vertical eye movements including the rostral
interstitial nucleus of the MLF (riMLF) and the interstitial
nucleus of Cajal (iC). While the riMLF is the immediate premotor
structure for the generation of torsional and vertical saccades,
the iC is considered a major part of the neural integrator for
torsional and vertical eye movements. Experiments in monkeys
show that a unilateral inactivation of the riMLF with muscimol
leads to spontaneous contralesional torsional nystagmus, whereas
an iC inactivation causes ipsilesional torsional nystagmus.
In addition, inactivation of either structure leads to a tonic
ocular torsion to the contralesional side. While the deficits
after a riMLF lesion are thought to result from an imbalance
of the saccade generator, a vestibular imbalance probably causes
the deficits after an iC lesion. Contralesional and ipsilesional
torsional nystagmus is also found in patients with unilateral
mesencephalic lesions. A detailed analysis of the lesions from
MRI scans shows a preferential involvement of the riMLF for
patients with contralesional torsional nystagmus, and a major
involvement of iC in cases with ipsilesional torsional nystagmus.
Thus, the direction of torsional nystagmus appears to be a valuable
topodiagnostic sign for patients with midbrain lesions.
