Organizing principles of cortical integration in the rat neostriatum: corticostriate map of the body surface is an ordered lattice of curved laminae and radial points.

The neuroanatomic organizing principles underlying integrative functions in the striatum are only partially understood. Within the three major subdivisions of the striatum-sensorimotor, associative, and limbic--longitudinal zones of axonal plexuses from the cerebral cortex end in bands and clusters that innervate cell groups. To identify organizing principles of the corticostriate bands and clusters, we localized somatosensory cortical cells receptive to light touch on the hindlimb, forelimb, or vibrissae by extracellular recording, and we labeled their projections by iontophoretic application of dextran anterograde tracers. The results show that cortical cells in columnar groups project to the striatum in the form of successive strips, or laminae, that parallel the curve of the external capsule. The vibrissae somatosensory cortex projects to the most lateral lamina. Just medial to the vibrissae projection, the major axonal arborizations arising from hindlimb and forelimb somatosensory cortex are organized within a common lamina, where they interdigitate and overlap as well as remain separate. In addition, the hindlimb and forelimb cortex send small projections to the vibrissae lamina, and vice versa, forming broken, radially oriented lines of points across the laminar strips. The major somatosensory projections are in the dorsolateral, calbindin-poor sensorimotor striatum, whereas the radially oriented projection points extend into the medial, calbindin-rich associative striatum. Extending previous studies of corticostriate projections, this report shows a grid translation of columnar somatosensory cortical inputs into striatum and a detailed map for the rat sensorimotor zone. The lattice-like grid is a novel functional/neuroanatomic organization that is ideal for distributing, combining, and integrating information for sensorimotor and cognitive processing.