Duke Neurobiology
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Laboratory of William C. Hall, Ph.D.MainLab PersonnelRecent Papers
Understanding the mechanisms responsible for the translation of sensory signals into the commands for movement is one of the fundamental goals of neurobiology. We are using in vitro whole-cell patch clamp recording in combination with photostimulaation with "caged" glutamate to study these mechanisms in the superior colliculus. Our results indicate that circuitry preserved within the slice is capable of generating bursts of action potentials that resemble the command bursts for orienting movements of the head and eyes The preservation of this circuitry in the slice gives us an opportunity to analyze sensorimotor mechanisms within the colliculus with a precision never possible before. Our results thus far indicate that the membrane properties of the cells are not responsible for the bursts but, instead, the circuitry intercalated between the superficial, or visuosensory, and the intermediate, or sensorimotor, layers enhances and prolongs the responses of premotor cells to even a transient input from the visual layer. Such transient signals might be provided in vivo by the sudden onset or movement of an object in the visual field. This amplification of the inputs to the intermediate layer into command signals for orienting movements may be one of the primary functions of collicular circuitry. We are using the same approach to examine horizontal connections within the intermediate gray layer. These experiments are designed to test the idea that short range recurrent excitation and long range inhibition mediate a "winner-take-all" competition among populations of premotor cells that generate the spatially encoded command signals for orienting movements to competing sensory targets. Our results indicate that horizontal inhibition is even more restricted spatially than excitation. Short-range inhibition is consistent with the hypothesis that the lateral inhibition plays a role in modulating the duration of responses in the intermediate layer, but is not consistent with a role for lateral inhibition in a wide-ranging competitive mechanism.

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