Conscious sensation and cognition depend upon the interaction of sensory areas with the rest of the cerebral neocortex. Like cats and monkeys, the areas of cerebral cortex in rats are reciprocally interconnected with asymmetrical patterns of forward/backward termination. The forward projections from primary sensory areas terminate in middle layer of higher order areas while the backward projections from those higher areas terminate most heavily in layer I of the primary area and avoid the zone in middle layers where the thalamocortical inputs terminate (Cauller, Clancy and Connors, 1998). Unlike the spatial topography characteristic of thalamocortical maps, the backward inputs extend horizontally within layer I such that every point in the primary topography shares layer I inputs with nearly all other points. In this way, backward or 'top-down' cortical influences are distributed across the primary topography similar to the non-topographic olfactory cortex or a Kohonen network. The layer I inputs terminate upon the distal apical dendrites of the pyramidal neurons of layers II/III and V which are in turn the origin of the forward cortico-cortical and the corticobulbar projections, respectively. In this way, the backward influences of the higher cortical areas are projected down to the brainstem structures controlling directed eye-movements and probing finger movements.