Cervico-ocular Reflex (COR) in Cervicogenic Dizziness

In contrast to the VOR, the COR responds optimally to head movements with a low velocity. This is much different than testing the VOR, such as the head thrust test, in which the head is moved in a high velocity method in rotation. Makes sense right with compensation--- if you lose your fastest player on your team due to a red card, you can still function with a different game plan.

HOW CAN YOU TAKE THIS INFORMATION TO TREAT YOUR PATIENTS?

This could make a difference in treating a patient with both a vestibular and cervical issue in regards to speed of training with vestibular and cervical movements to maximize what can be improved via habituation in daily life. As a clinician, you may want to include both high and low velocity head/neck movements through a progressive sensorimotor training program, if necessary, to maximize outcomes.

One of the beautiful phenomenons behind reflexes, especially ones that overlap to compensate for function of the body, is the ability to take on the lost function during specific tasks. This is very important in maintaining body balance, especially as we age. This is a pretty awesome compensation pattern and highlights the importance of the human nervous system to be able to adapt via neuroplasticity.

• This is seen in patients with vestibular deficiencies/losses/absences where the cervico-ocular reflex takes the control of function during the loss of the vestibulo-ocular reflex (Bronstein & Hood 1986, Heimbrand 1996).

• This can be seen with labyrinth defective persons and with increasing age, where the vestibular function deteriorates (just like any other organ) so may be something to think about while treating your older patients who may have "plateaued" with vestibular function.

• You can also relate this to a patient with whiplash-associated disorder or even in someone with reduced neck mobility, where an increase in COR gain with reduced neck mobility and lack of synergy between VOR and COR (Kelders et al 2005, Montfoort et al 2008).

• Moreover, a change in COR does not have to just come from traumatic neck pain, but has been shown to be increased in non-specific neck pain (de Vries et al 2016).

• Interestingly enough, just a use of a stiff neck collar to immobilize the neck (think general muscle stiffness/guarding) has been shown to modify the strength of the COR (Montfoort et al 2008).

• Even more specifically, in a group of patients with limited C1-2 mobility as tested via the flexion-rotation test, Zamyslowska-Szmytke et al 2019 found that patients with asymmetric restriction in neck rotation and increased neck muscle tension reveal the tendency to have an increased response in the vestibular system, with co- existing asymmetric COR upregulation.

• For some of your patients with dizzy and/or neck pain, a typical approach of canalith repositioning procedures, vestibular rehabilitation or cervical therapeutics can address the problem. However, we find that the clinicians who benefit most from this knowledge, and even our class, are the ones looking to help the patients who do not "fit" the protocol-based therapy and manual therapy, but need more tools to the tool-box to learn how to combine therapeutics of the vestibular, cervical and sensorimotor systems to give better results to their patients.

If the patient who has a disturbed vestibular system or with increase in age, he or she may have to rely more heavily on the COR due to impairment of the other stabilization reflexes (Kelders et al 2003). If a patient has nonspecific neck pain, then an increase in COR can occur (de Vries et al 2016). Ultimately, a patient with dizziness and neck pain most likely has both of the above scenarios.

Therefore, if pain, trauma or altered movement strategies in the cervical spine alter the afferent input to the vestibular nuclei and other central organs, this compensation strategy has now become impaired and ultimately the perfect storm could arise with symptoms such as dizziness, lightheadiness, unsteadiness or drunkenness.

We think of this concept as we do with other compensation patterns in the body, through a credit section and debit section. For a simplistic description, when one system (i.e. vestibular = VOR) goes down in the red, we need to step up our game so another system (i.e. cervical = COR) to pick up the slack. We have to re-calibrate and keep maintenance so we don't dip too deep in the debit section and go bankrupt.

We "address" these reflexes with a combined manual therapy, vestibular and sensorimotor approach in our Physio Blend. As clinicians, we do not visually change these reflexes, but do feel it is best if the vestibular and orthopedic therapist knows about them in order to improve involuntary control of the head on neck with your dizzy and neck pain patients. If your hypothesis is one in which one system (such as vestibular) is down-regulated due to pathology, then another system (such as cervical) is up-regulated. This works well until all systems are in the dump!

For the purpose of this blog, this is a basic understanding of reflexes, locomotion, postural control and static/dynamic head on neck control. We think this is enough pertinent information for the day to day clinician that we teach (and also do as clinicians) to give you an idea of what may go on neurologically with disturbances with the visual, vestibular and cervical systems. For more information, we do recommend reading several other pieces of literature to delve further, especially the works of Morningstar, et al 2005, and Kelders, et al 2003.