Research Description

The goal of my research is to understand how sensory vestibular signals are processed by the brain, and in particular how these signals are used in the control of eye and head movements.

The vestibular apparatus generates signals that are related to the movement and position of the head in space. The brain uses these sensory signals to estimate the orientation of the head in space and to help maintain posture and balance. One problem that we have been studying is how signal processing in the vestibular pathways that function to maintain steady head position or gaze are modified when we want to actively move our head or eyes. We recently found that vestibulo-spinal pathways that function to stabilize neck posture and vestibulo-ocular pathways that function to stabilize images on the retina are not sensitive to vestibular signals related to active head movements. The observations suggest that the brain treats incoming vestibular sensory information differently, depending on whether the head movement that produces the sensory signal is intentional or not. On further examination we found that this differential treatment occurs primarily by comparison of vestibular inputs with central intentional commands and peripheral neck proprioceptive signals. The latter signals "cancels" sensory signals related to voluntary head movements, without affecting the ability to detect external, unintentional perturbations of the head.

The question we are currently asking is how cancellation of self-generated vestibular signals occurs. One possibility is that neck proprioceptive inputs or central neural neck motor signals modify sensory processing in the vestibular nuclei or vestibular regions of the cerebellum or cerebral cortex. We are examining this idea by selectively stimulating neck and body proprioceptors in ways that mimic their activation during voluntary head movements and by studying the firing behavior of neurons in the vestibular nuclei, the cerebellar cortex and the cerebral cortex during isometric and variable resistive head movements. A second possibility is that the signals produced by the labyrinthine receptors and neural elements that innervate them are modified by vestibular "efferent" neural pathways from the brain to the labyrinth. Jay Goldberg and I are studying the firing behavior of this pathway in alert monkeys trained to generated active and passive head movements. A third possibility is that the central processing of vestibular signals is modified by parametric adjustment of vestibular nerve synaptic inputs to central neurons. We have been studying this by selectively and reversibly ablating or stimulating different classes of vestibular afferents and observing the effects of these reversible "lesions" on signal processing in the vestibular nuclei and on behavior.

Recently, we used the selective ablation technique in squirrel monkeys to study the parametric changes in the vestibulo-ocular reflex that occur as a function of viewing distance. We found that the ability to increase the speed of the eye movements when the head moves while focusing on a near visual target depends on a specific class of vestibular nerve inputs which are allowed to affect vestibulo-ocular reflex pathways only when near objects are being viewed.

In sum, the focus of my research has been to try to unravel how the signal processing in vestibular postural control circuits is modified from moment to moment, depending on the behavioral context. Our future plans are to study the physiology of this context dependent sensory processing in alert behaving primates. 

top