Two types of ocular tilt reaction: the ‘ascending’ pontomedullary VOR-OTR and the ‘descending’ mesencephalic integrator-OTR

Abstract

Ocular tilt reaction (OTR) is a fundamental pattern of eye-head coordination in roll and is elicited by unilateral lesions on the peripheral and central vestibular ‘graviceptive’ pathways from the otoliths and the vertical semicircular canals to the rostral midbrain integration center. We propose the following differentiation between two types of OTR: (1) the ‘ascending’ pontomedullary VOR-OTR with ipsilateral lesions of the vestibulo-ocular reflex pathways in roll, from the labyrinth to the vestibular nuclei. This type is characterized by disconjugate ocular torsion and occurs if anterior, posterior, or both semicircular canal and otolithic pathways are affected and (2) the ‘descending’ mesencephalic integrator-OTR with contralateral lesions of the rostral midbrain integration center (INC) for eye-head coordination in the roll plane. This type is characterized by conjugate ocular torsion. The ‘ascending, reflexive’ type (lateral medulla) of OTR simply reflects a tone imbalance of the VOR, whereas the ‘descending integration’ type (rostral midbrain tegmentum) integrates signals of eye-head velocity with those of holding position and involves cortical control of OTR during active locomotion. The frequent (pontomesencephalic) ‘skew torsion’ without head tilt results from contralateral lesions of crossing ascending ‘graviceptive’ pathways rostral to the downward branching of vestibulospinal connections. It does not cause head tilt, because vestibulospinal tracts are not involved at this site of the lesion.