Abstract
Introduction: To have stable vision during rapid head movements, the vestibulo-ocular reflex (VOR) is required. The VOR allows the eyes to remain fixated on a target during head rotations by moving the eyes in the opposite direction, at the same velocity, as the head rotation. This ensures that images are kept stable on the retina. For the eye movement to occur, the vestibular system transmits sensory information to the cerebellum to control the VOR. VOR gain is the ratio of head and eye velocity, in which any mismatch between this ratio leads to an adaptation of the VOR response. VOR adaptation is used to measure cerebellar processing and plasticity as it is directly controlled by the cerebellum. Subclinical neck pain can alter the sensory information received by the cerebellum, from the neck and vestibular system. Thus, individuals with SCNP may have altered cerebellar processing as demonstrated by alterations in the VOR.
Purpose: To determine the influence of SCNP on cerebellar plasticity by measuring the VOR gain adaptation.
Methods: This is a quasi-experimental study design. For examining VOR gain, both SCNP and asymptomatic groups were recruited. Participants were seated 90 cm away from the 30-inch monitor and perform bilateral head rotations while wearing an eye-tracker (Eye-Link-II) which recorded gaze angle and eye velocity during the motion. Head velocity was measured through Optotrak Certus cameras which tracked infrared markers that were attached to the eye-tracker. During head rotations, the participant's eyes were fixed on a target located on the screen. Head rotation was performed at an average velocity of 150 degrees/second with 20 degrees of amplitude. Participants performed 360 trials of head rotations within 12 blocks, with each block consisting of 30 trials. The 12 blocks were grouped into three different phases, consisting of a pre-adaptation block, 10 adaptation blocks, and a post adaptation block. In the adaptation blocks, the target moved in the opposite direction of the head rotation at a speed of 10% of head velocity and increased by increments of 10% for each subsequent block. The participant was asked to keep the head rotated until a white screen appeared at the 20-degree mark. Auditory feedback at the end of each trial was presented to ensure their head was moving at the desired pace to induce the VOR. Two low-pitched beeps indicated a head rotation of too slow, two high-pitched beeps indicated the head motion of too fast, and one medium pitch beep was an indication of the speed of the head rotation was of normal pace.
Results: Data analysis was completed on 7 participants (C = 3; SCNP = 4) (data collection halted due to Covid) and no statistical analysis was completed due to the small sample size and this only being pilot data. On average, control participants demonstrated a 14.5% increase in VOR gain from the pre-adaptation block to adaptation block 10, while SCNP participants only demonstrated a 0.04% increase in VOR gain. Control participants also demonstrated a 3.6% decrease in VOR gain from adaptation block 10 to the post-adaptation block. While SCNP participants demonstrated a 7.3% increase in VOR gain.
Conclusions: This preliminary data suggests that individuals with SCNP have a diminished ability to adapt their VOR. This would further suggest that individuals with SCNP have altered cerebellar processing compared to healthy controls.
