The experiments are designed to provide new and basic information about what happens in the central nervous system during learning, or when neural systems are excessively stimulated. Experiments on adult cats have shown that elements of pyramidal cells of the cerebral neocortex probably grow as a result of increased input to the cells. Efforts will be made to identify the morphologically changed neurons electrically, by observing their excitabilities or discharge properties after pathways leading to them have been activated for several weeks. Other experiments proposed are studies of undercut cerebral neocortex in cats. A cat loses its ability to give conditioned leg flexions to conditional brain stimulation when the stimulated area is surgically undercut. However, the cat can be retrained and thus the cortex gains a new intracortical transmission capability. Neurons of the cortical undercut will be studied histologically for their possible morphological changes as a result of the retraining. Further experiments will explore current densities in different parts of the undercut area. Knowledge of current densitites could provide a measure of the overall electrical activity of the neural tissue in small volumes, and could lead to new concepts about modified conduction in neural systems.