Parallel Cortical Pathways Through the Pulvinar/LP Complex

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LAY ABSTRACT Principal Investigator: Bickford, Martha Proposal Number: IBN- 9728089 PARALLEL CORTICAL PATHWAYS THROUGH THE PULVINAR COMPLEX Most sensory signals must pass through the dorsal thalamus before they are consciously recognized in the cortex. It has been known for a number of years that sensory signals from peripheral receptors are segregated, and travel in parallel pathways through the relay nuclei of the dorsal thalamus, to primary sensory areas of cortex. The study of parallel pathways in sensory system, particularly in the visual system, has provided a key to understanding how the brain codes the wide variety of incoming information. The realization that features such as color, motion, or contrast are coded by separate subcortical cell types has provided a valuable conceptual framework for studies of how visual signals are perceived by the brain. This proposal tests the hypothesis that similar parallel pathways exist in areas of the thalamus that associate information from a variety of cortical areas. In this case, the proposed parallel pathways originate in cortex, and remain segregated in the thalamus through synaptic contacts on distinct classes of thalamocortical neurons, which project to different cortical laminae. This idea will be tested in the pulvinar and lateral posterior nuclei, which receive input from two types of layer V cortical cells, and contain at least two morphologically distinct types of thalamocortical cells. It is proposed that separate cortical axons contact separate classes of thalamocortical cells that project to different cortical lamina. The proposed anatomical experiments, which involve the injection of neuroanatomical tracers and irnmunocytochemistry, wi ll test the concept that parallel pathways are utilized in the processing of internal cortical signals. It is anticipated that, similar to the study of parallel sensory pathways, this information will provide a fruitful starting point for deciphering the function of the pulvinar and lateral posterior nuclei.