EARLY EXPERIENCE AND ADULT CORTICAL PLASTICITY

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The study of local circuits in cerebral cortex has relied on physiological measures of the responses of single neurons to stimulation. The obvious missing ingredient in current approaches to cortical function is the ability to study the normal function of large groups of neurons working together. We have developed an experimental procedure which makes it possible, for the first time, to study the metabolic activity of every immunohistochemically labeled neuron in a neural system of interest. The procedure combines a high-resolution 2-deoxyglucose (2DG) technique, immunostaining for glutamate decarboxylase (GAD) and other antigens, and extensively automated data collection and analysis. These materials allow a direct assessment of the extent of excitation and inhibition in individual neurons. We propose to make extensive use of this double-labeling technology to study local circuitry in the whisker- related barrel field of rodent somatosensory cortex. We will quantitatively map and analyze the cellular patterns of cortical 2DG labeling seen in behaving hamsters and mice. We will compare cortices from normal, acutely whisker-trimmed, artificially stimulated, and chronically whisker-trimmed rodents with respect to the underlying distribution of GAD and other immunostains. We will generate complete high resolution functional maps of the stimulated and surrounding portions of the barrel field, enabling accurate comparison of the metabolic activities in antigenically defined compartments across the cortex. From the database represented by these maps, we will test a number of specific hypotheses about cortical function and information flow in the trigeminal system of the behaving animal. A detailed comparison of our previous 2DG data and predictions derived from single-unit physiology shows good agreement despite vast differences in the two methods. We will pursue this line of evidence by looking for parallels in 2DG/immunostained materials to functional groups of neurons that have been physiologically characterized by other workers. We will then examine by anatomical means the projection fields of excitatory and inhibitory populations of neurons, and correlate the results of these measures with the extent of excitation and inhibition in individual neurons with different combinations of stimulated whiskers. We will assess the specific contribution of cortical and subcortical circuitry by comparing the activation patterns in various stations of the trigeminal pathway with the patterns of whiskers remaining on the face. Finally, we will characterize the plasticity in barrel cortex by comparing the normal patterns of cortical labeling with those observed following prolonged deprivation (whisker trimming) or artificial whisker stimulation.