Verticality perception in patients with lesions along the graviceptive pathways: acute deficits and subsequent compensation

Abstract

Bilateral central vestibular pathways (CVP) send signals from the vestibular nuclei to the cerebellar, brainstem, and cortical areas that are involved in processing graviceptive signals. Whereas the estimated direction of gravity is accurate when upright, systematic angle-dependent errors can occur when roll-tilted: over-estimations at small and very large roll angles (E-effect) and roll under-estimation at medium-sized roll angles (A-effect). Acute lesions along the CVP frequently lead to deviations of the subjective visual vertical (SVV). Whereas SVV errors in upright positions have been well characterised, changes in the A- and E-effect and in SVV precision due to lesions along the CVP have not been studied in roll-tilted positions. We report on a series of patients with CVP lesions and compare SVV measurements in different roll orientations (0°, ±45°, ±90°) in the sub-acute state (4–33d) with follow-up ~4 months later. In an upright position, 5/6 patients showed SVV deviations in the sub-acute state; in 3 patients deviations were ipsilesional. When rolltilted, 4/6 patients showed increased SVV errors. In all patients, the pattern of SVV errors could be explained by combining an SVV offset in an upright position with body-position-dependent errors when roll-tilted, being larger on the ipsilesional side and smaller on the contralesional side or vice versa. SVV precision was decreased in 4 patients. After 4 months, verticality perception was either improved (n = 1) or within normal range (n = 2) in terms of accuracy and precision in 3/4 patients. These results show that lesions along the CVP result in altered estimates of the direction of gravity in the entire roll plane, which can improve within a few months due to central compensation. At the time, accuracy had normalised in upright positions, estimated direction of gravity when roll-tilted could still be erroneous. Assessing the SVV in roll-tilted positions may reveal more subtle deficiencies and may hence support continuation of balance physiotherapy.