February 15, 2013
Vestibular-Ocular Reflex Is More Sophisticated Than Previously Believed
Michael Harper for redOrbit.com — Your Universe Online
Our brains are capable of doing some amazing things. Yet, there are some processes which, while sophisticated enough, are mostly thought of as common and basic. For instance: The reflex which allows us to keep our eyes focused on one point while our heads are moving about. This reflex is called the Vestibular-Ocular Reflex (or VOR), and we share it with most vertebrates.For many years, scientists have believed that this reflex is controlled in the lower brainstem as a low-level process without much sophistication. Now, researchers from at the Imperial College in London are challenging this notion, suggesting that this reflex is controlled by higher-level functions, such as those which determine handedness. This research has resulted in a paper which has been published in the Journal of Neuroscience.
To better understand where this VOR process takes place, Qadeer Arshad and his colleagues sat volunteers on spinning chairs and showed them a series of optical illusions. These motorized chairs spun at a speed of 1 rotation every 4 seconds. As these subjects were spinning, researchers measured how long it took their eyes to adjust to the spinning.
The subjects were then shown a series of bistable visual phenomena. These images are optical illusions which appear to switch between 2 different images, such as the duck which also appears to be the duck or the candlestick which also looks like two people facing one another. Scientists believe a higher-level portion of the brain is responsible for detecting these images and making sense of them. Therefore, Arshad and team were not expecting to find any link between VOR and this high-level process.
These researchers were surprised, then, when the volunteers had difficulty focusing their gaze on these images as they were spinning. The direction which these subjects were looking depended on their handedness, as well. Right handed volunteers followed a rightward rotation, and vice versa.
“This is the first time that anything of this kind has been shown. Up until now, the Vestibular-Ocular Reflex was considered a low-level reflex, not even approaching higher-order brain function. Now it seems that this primitive reflex was specialized into the cortex, the part of the brain which governs our sense of direction,” explained Arshad in a statement detailing his latest work.
Arshad said this study can be used to understand why people sometimes get dizzy solely by visual stimuli, such as flickering lights or crowded aisles in a grocery store.
“Most causes of dizziness start with an inner ear - or vestibular - disorder but this initial phase tends to settle quite rapidly. In some patients, however, dizziness becomes a problematic long term problem and their dizziness becomes visually induced. The experimental set-up we used would be ideally suited to help us understand how visual stimuli could lead to long-term dizziness. In fact, we have already carried out research at Imperial around using complex visual stimuli to treat patients with long-term dizziness,” explained Bronstein.