Book excerpt: Sensory signals reach the cerebral cortex after having made synapses in different relay stations along the sensory pathway. The flow of sensory information in subcortical relay stations is controlled by the action of precise topographic connections from the neocortex. Several lines of research indicate that the massive corticifugal system improves ongoing subcortical sensory processing and reorganizes the receptive fields in visual, auditory and somatosensory systems. In all these sensory systems cortical neurons mediate both the highly focused positive feedback to subcortical neurons with ove.