INPUT/OUTPUT RELATIONSHIPS IN VISUAL CORTEX

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The proposed experiments investigate the relationship between the pattern of termination of various types of afferents and the pattern of dendritic arborization of neurons that project to different targets. The two specific questions being posed are: 1) Do cortical neurons with different efferent targets have different patterns of dendritic arborization? 2) How do different sources of afferents terminate with respect to those patterns of arborization? This study will be carried-out in cat Posterior Medial Lateral Suprasylvian Sulcus (PMLS), a visual area with diverse sources of afferents as well as multiple cortical and subcortical efferent targets. The first question will be approached using a lightly fixed slice preparation to intracellularly inject layer V neurons that have been retrogradely labeled from three regions known to play different roles in the processing of visual information, the superior colliculus, pons, and ipsilateral striate cortex. The dendritic morphologies of neurons that project to these areas will be compared in order to determine if there are differences in patterns of afferent sampling. Neurons that project to two of these sites, via collaterals, will also be retrogradely labeled and intracellularly injected in order to determine if they are morphologically distinct from the neurons that project to only one of the two sites. The second question will be approached by making separate sets of iontophoretic injections of anterograde tracer into three regions thought to be responsible for the unique physiological properties of PMLS neurons, the lateral posterior/pulvinar complex, the intralaminar nuclei, and the ipsilateral striate cortex. Anterogradely filled axons and their boutons will be drawn and their distribution compared with the different dendritic patterns of layer V projecting neurons. By studying the relationship of input to output neurons in PMLS, it is hoped that the results will contribute to an understanding this region's role in visuomotor behavior.