Complementary gain modifications of the cervico-ocular (COR) and angular vestibulo-ocular (aVOR) reflexes after canal plugging

Abstract

To determine whether the COR compensates for the loss of aVOR gain, independent of species, we studied cynomolgus and rhesus monkeys in which all six semicircular canals were plugged. Gains and phases of the aVOR and COR were determined at frequencies ranging from 0.02 to 6 Hz and fit with model-based transfer functions. Following canal plugging in a rhesus monkey, the acute stage aVOR gain was small and there were absent responses to thrusts of yaw rotation. In the chronic state, aVOR behavior was characterized by a cupula/endolymph time constant of ≈0.07 s, responding only to high frequencies of head rotation. COR gains were ≈0 before surgery but increased to ≈0.15 at low frequencies just after surgery; the COR gains increased to ≈0.4 over the next 12 weeks. Nine weeks after surgery, the summated aVOR + COR responses compensated for head velocity in space in the 0.5–3 Hz frequency range. The gains and phases continued to improve until the 35th week, where the combined aVOR + COR stabilized with gains of ≈0.5–0.6 and the phases were compensatory over all frequencies. Two cynomolgus monkeys operated 3–12 years earlier had similar frequency characteristics of the aVOR and COR. The combined aVOR + COR gains were ≈0.4–0.8 with compensatory phases. To achieve gains close to 1.0, other mechanisms may contribute to gaze compensation, especially with the head free. Thus, while there are individual variations in the time of adaptation of the gain and phase parameters, the essential functional organization of the adaption to vestibular lesions is uniform across these species.

Compensation Following Bilateral Vestibular Damage

“…In contrast, many of the neurons that control balance (Nyberg-Hansen and Mascitti, 1964; Petras, 1967; Peterson et al, 1978; Carleton and Carpenter, 1983; Carpenter, 1988) and influence blood pressure (Uchino et al, 1970; Yates et al, 1993; Kerman and Yates, 1998) are located caudally in the vestibular nucleus complex. In addition, the major components of vestibulo-ocular reflexes are dependent on inputs from semicircular canals (Money and Scott, 1962; Suzuki and Cohen, 1964, 1966; Baker et al, 1982; Hess et al, 2000; Sadeghi et al, 2009; Yakushin et al, 2011). Although data are limited, at least some cognitive responses related to vestibular inputs also appear to require inputs from semicircular canals (Muir et al, 2009).…”

The influence of cervical movement on eye stabilization reflexes: a randomized trial

“…Both reflexes are indeed quite plastic, in the sense that they adapt to perturbations and changes of input. In laboratory settings, it has been observed that the VOR and COR adapt to experimentally perturbed visual and vestibular input (Schweigart et al 2002;Rijkaart et al 2004;Montfoort et al 2008;Yakushin et al 2011). However, little is known about the adaption of the reflexes to perturbed cervical input.…”

Spatial orientation of the angular vestibulo-ocular reflex (aVOR) after semicircular canal plugging and canal nerve section

“…The early loss of response is probably due to detachment of the cupula from the roof of the ampulla, with reattachment at a later time, as found in the toadfish (Rabbitt et al 1999, 2009). The changes in gain over time in the toadfish are similar to responses to sinusoidal oscillation in the rhesus monkeys (Yakushin et al 2011). As our results demonstrate, there were no changes in spatial orientation of the canal responses after canal plugging, whether from single canals or from all six canals.…”

“…The responses obtained within the first week after canal plugging (acute state) were low in some animals, but they recovered to levels predicted by the model of the aVOR after several weeks (chronic state) (Yakushin et al 2011). The early loss of response is probably due to detachment of the cupula from the roof of the ampulla, with reattachment at a later time, as found in the toadfish (Rabbitt et al 1999, 2009).…”