Posts tagged vestibular system
Articles and news from the latest research reports.
Neurologists at LMU have studied the role of the vestibular system, which controls balance, in optimizing how we direct our gaze. The results could lead to more effective rehabilitation of patients with vestibular or cerebellar dysfunction.
When we shift the direction of our gaze, head and eye movements are normally highly coordinated with each other. Indeed, from the many possible combinations of speed and duration for such movements, the brain chooses the one that minimizes the error in reaching the intended line of sight. Dr. Nadine Lehnen, who heads a research group based at LMU’s Center for Vertigo and Balance Disorders, in collaboration with her colleague Dr. Murat Saglam and Professor Stefan Glasauer of the Center for Sensorimotor Diseases at LMU, have now published a paper in the latest issue of the journal of Brain which investigates the significance of the vestibular system for this optimization of motor coordination. The vestibular system in the brain is mainly responsible for the maintenance of balance and posture. The new work focused on subjects suffering from bilateral defects in the vestibular system (a complete vestibulopathy) or lesions in the cerebellum, which is functionally linked to it.
The authors of the new study had previously developed a mathematical model that enabled them to predict the horizontal movements of the head and eyes in response to the presentation of an off-center stimulus. “When subjected to repeated trials, healthy subjects are able to select the combination of eye and head movements that minimizes gaze shift variability,” says Glasauer. They unconsciously choose the set of movements associated with the least error in the endpoint. Moreover, they can do this even when wearing a helmet with weights attached, which alters the moment of inertia of the head.
Learning to find the endpoint
However, patients who show defects in the vestibular system or the cerebellum have greater difficulty in controlling the direction of gaze in response to changes in their environment. “It turns out that information relayed from the balance organs to the vestibular system is essential for the optimization of gaze shifts,” says Nadine Lehnen. Patients with complete bilateral vestibular loss are therefore unable to perform such shifts in the most efficient way. “In striking contrast, patients with cerebellar damage can, to a certain extent, learn to optimize certain parameters of head and eye movements, by adjusting the velocity of head movement, for instance,” says Glasauer.
"These results provide the first evidence that the vestibular system is critical for optimizing voluntary movements“, says Dr. Kathleen E. Cullen from McGill University in Montreal in a scientific commentary to the study appearing in the print issue of Brain. The new findings are of relevance for the rehabilitation of patients who have suffered damage to the cerebellum and patients with incomplete vestibulopathies. “We assume that gaze shift control in these patients can be enhanced by a rehabilitation training based on active head movements,” says Nadine Lehnen. Head movements provide the vestibular feedback which generates the sensorimotor error messages that underlie the ability to learn how to optimize the coordination of eye and head movements. Instead of trying to hold their heads steady, these patients should be encouraged to actively move their heads, when they shift their gaze.
The question if patients with partial vestibulopathy can optimize gaze shift behavior by engaging in active head movements is now under investigation. This work forms part of a rehabilitation study which is being carried out at the Center for Vertigo and Balance Disorders at Munich University Hospitals, and is financed by the Federal Ministry for Education and Research.
Decoding the secrets of balance
July 25, 2012
(Medical Xpress) — New understanding of how the brain processes information from inner ear offers hope for sufferers of vertigo.
If you have ever looked over the edge of a cliff and felt dizzy, you understand the challenges faced by people who suffer from symptoms of vestibular dysfunction such as vertigo and dizziness. There are over 70 million of them in North America. For people with vestibular loss, performing basic daily living activities that we take for granted (e.g. dressing, eating, getting in and out of bed, getting around inside as well as outside the home) becomes difficult since even small head movements are accompanied by dizziness and the risk of falling.
We’ve known for a while that a sensory system in the inner ear (the vestibular system) is responsible for helping us keep our balance by giving us a stable visual field as we move around. And while researchers have already developed a basic understanding of how the brain constructs our perceptions of ourselves in motion, until now no one has understood the crucial step by which the neurons in the brain select the information needed to keep us in balance.
The way that the brain takes in and decodes information sent by neurons in the inner ear is complex. The peripheral vestibular sensory neurons in the inner ear take in the time varying acceleration and velocity stimuli caused by our movement in the outside world (such as those experienced while riding in a car that moves from a stationary position to 50 km per hour). These neurons transmit detailed information about these stimuli to the brain (i.e. information that allows one to reconstruct how these stimuli vary over time) in the form of nerve impulses.
Scientists had previously believed that the brain decoded this information linearly and therefore actually attempted to reconstruct the time course of velocity and acceleration stimuli. But by combining electrophysiological and computational approaches, Kathleen Cullen and Maurice Chacron, two professors in McGill University’s Department of Physiology, have been able to show for the first time that the neurons in the vestibular nuclei in the brain instead decode incoming information nonlinearly as they respond preferentially to unexpected, sudden changes in stimuli.
It is known that representations of the outside world change at each stage in this sensory pathway. For example, in the visual system neurons located closer to the periphery of the sensory system (e.g. ganglion cells in the retina) tend to respond to a wide range of sensory stimuli (a “dense” code), whereas central neurons (e.g. in the primary visual cortex at the back of the head tend to respond much more selectively (a “sparse” code). Chacron and Cullen have discovered that the selective transmission of vestibular information they were able to document for the first time occurs as early as the first synapse in the brain. “We were able to show that the brain has developed this very sophisticated computational strategy to represent sudden changes in movement in order to generate quick accurate responses and maintain balance,” explained Prof. Cullen. “I keep describing it as elegant, because that’s really how it strikes me.”
This kind of selectivity in response is important for everyday life, since it enhances the brain’s perception of sudden changes in body posture. So that if you step off an unseen curb, within milliseconds, your brain has both received the essential information and performed the sophisticated computation needed to help you readjust your position. This discovery is expected to apply to other sensory systems and eventually to the development of better treatments for patients who suffer from vertigo, dizziness, and disorientation during their daily activities. It should also lead to treatments that will help alleviate the symptoms that accompany motion and/or space sickness produced in more challenging environments.
Provided by McGill University
Source: medicalxpress.com