Neural Control of Eye-head Movements

Figure 1. Head, eye, and gaze position are plotted as functions of time during a 60 degree gaze shift composed of coordinated movements of the eyes and head. The head contributed ~10 degrees to the overall change in gaze direction during this movement. The remaining 50 degrees of the gaze shift were accomplished by the saccadic eye movement. Note that when the line of sight is directed toward the new location (gaze end) that the head continues to move. Gaze position in space remains constant during this epoch due to equal and opposite eye counter-rotation mediated through the VOR.

Maintaining our sense of the world around us and being able to interact with our environment depends in large part on the nervous system’s ability to perform a few basic functions. We must be able to gather accurate sensory information about our surroundings, distinguish our movements from the movements of objects in the world, and coordinate our own movements in order to orient, and navigate smoothly through a complex setting. Vision, audition and somatosensation provide information about objects in the world, information about self movement is provided through the vestibular and proprioceptive systems. This wealth of sensory information must be integrated into a unified representation of objects including our own bodies. This neural representation of the environment can then be used to plan and implement behaviors which allow us to manipulate and interact with objects of interest. For example, we might hear or see an object in the periphery, and in order to visually localize and identify the object we need to plan and execute a movement which will re-direct our line of sight. To accomplish this task (which we do more than 125,000 times a day) we need to assess the object’s location based on either the visual or auditory inputs. Then we must compute the difference between our current line of sight and the position of the target, incorporate information about the capabilities of the body segments which will contribute to moving the line of sight (e.g. the mobility of the eyes and head given their current positions), and coordinate more than 40 muscles and muscle groups to smoothly look at the target. Although we generally take this type of computationally intensive behavior for granted, even minor failures can cause a drastic reduction in our ability to function adequately in the world.

My approach to understanding these critical brain functions focuses on issues of sensori-motor integration and the neural computations necessary to plan and execute coordinated movements. In particular, using psychophysical and neurophysiological techniques, research in my lab addresses the neural mechanisms which result in the control and coordination of visual orienting behaviors. We are currently studying the role of the brainstem in eye-head coordination, cerebellar contributions to eye-head movements and motor learning processes, and the interactions between cerebellum and brainstem regions involved in control of visual orienting. In addition, we are expanding our interests in eye-head coordination in a study involving human subjects investigating the ability to adapt motor output based on changed visual inputs, and the effects of aging on eye-head coordination. These studies will facilitate a clearer understanding of the neural mechanisms that mediate the control of coordinated movements.

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