Smooth pursuit (SP) eye movements are used to maintain the image of a moving object on or near the fovea. The SP system is able to adapt to challenges associated with development or injury to maintain pursuit accuracy and clear vision. Short-term adaptation of SP can be produced experimentally using a step-ramp pursuit paradigm where target speeds changes during ongoing pursuit. Previous studies demonstrate that the macaque cerebellum plays an essential role in adaptive changes of SP. However, the sources of signals for smooth pursuit adaptation have not been fully defined. Our studies are directed at structures that form important parts of the afferent limb for smooth pursuit. These structures include cortical-pontine and cortical-pretectal pathways that provide visual- and eye-motion signals to the cerebellum for smooth pursuit. We will determine the response properties of neurons in medial superior temporal (MST) cortex and dorsolateral pontine nucleus (DLPN), nucleus reticularis tegmenti pontis (NRTP) and pretectal nucleus of the optic tract (NOT) before, during and after smooth pursuit adaptation. We will test the hypothesis that area MST, NRTP and DLPN provide different eye movement signals that interact with visual motion signals provided by the NOT to produce direction selective adaptation. We will use a step-ramp behavioral paradigm where ramp speed either steps-up or steps-down during tracking to produce adaptation. We will use electrical stimulation and pharmacological inactivation of these centers to test their relative importance in pursuit adaptation. Our studies will significantly advance our understanding of information processing in important smooth pursuit centers related to adaptive plasticity. Understanding how the brain adapts smooth pursuit behavior in the face of challenges associated with development, aging or injury is important for improving diagnosis and treatment options for subjects with impaired visual-oculomotor function.
Humans depend on the fovea for high acuity visual function. The oculomotor system is responsible for placing the image of an object of interest on the fovea. When the subject or object moves, smooth pursuit eye movements are used to hold the image relatively stable to permit full visual function. Challenges associated with development, aging and injury of the brain require adaptive capability to preserve visual and eye movement function. Our studies are designed to determine neuronal mechanisms responsible for adaptive plasticity in the smooth pursuit system. New knowledge obtained in our research could help improve diagnosis and treatment options for different neurological disorders including those associated with stroke and neurodegenerative diseases.
