Plasticity of the cervico-ocular reflex in health and Disease

Abstract

The cervico-ocular reflex (COR) is an ocular stabilization reflex that is elicited by rotation of the neck. It works in conjunction with the vestibulo-ocular reflex (VOR) and the optokinetic reflex (OKR) in order to prevent visual slip over the retina due to self motion. The VOR and OKR decrease with age. We investigated whether the COR shows a compensatory increase and whether a synergy exists between the COR and the other ocular stabilization reflexes. We found that the COR gain increases with rising age and that there is a significant covariation between the gains of the VOR and COR, meaning that when VOR increases, COR decreases and vice versa. We also investigated whether the COR can be adapted by inducing a mismatch between vision and neck proprioception, in analogy to VOR adaptation. Analysis showed a small but significant reduction in COR gain in the suppression conditions. Also COR measurements were done in whiplash patients. To date there is no generally accepted test that allows an objective diagnosis of whiplash associated disorder (WAD). Because whiplash injury causes dysfunction of proprioception in the neck, we investigated the characteristics of the COR of presumptive WAD patients. Their COR was significantly increased compared to healthy subjects. Then we investigated whether the reported elevation of the COR in whiplash injury patients is accompanied by changes in VOR and / or OKR gains. We confirmed a significant increase in COR gain in whiplash patients but no change in VOR or OKR. This is in contrast with earlier observations in elderly and labyrinthine defective subjects. An impaired neck motion, altered proprioception of the neck or disorganization in the process of VOR plasticity could explain the lack of change in VOR gain. We conclude that the quickly adaptable and age dependent COR is a sensitive instrument to differentiate whiplash injury patients from healthy controls. Even though, further measurements with larger numbers of both patients and controls have to be conducted to establish whether more forms of cervical pain produce a rise in COR gain and to try and establish a cut-off point for WAD patients