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Using optical methods through a closed cranial window over the rat primary sensory cortex in chloralose/urethane-anesthetized rats we evaluated the time course of oxygen delivery and consumption in response to a physiological stimulus (whisker deflection). Independent methodological approaches (optical imaging spectroscopy, single fiber spectroscopy, oxygen-dependent phosphorescence quenching) were applied to different modes of whisker deflection (single whisker, full whisker pad). Spectroscopic data were evaluated using different algorithms (constant pathlength, differential pathlength correction). We found that whisker deflection is accompanied by a significant increase of oxygenated hemoglobin (oxy-Hb), followed by an undershoot. An early increase in deoxygenated hemoglobin (deoxy-Hb) proceeded hyperoxygenation when spectroscopic data were analyzed by constant pathlength analysis …