The organization of the projection from the cerebral cortex to the striatum in the rat.

The detailed organization of the corticostriate projection has been investigated in the brain of the rat using the technique of retrograde transport of horseradish peroxidase following the placement of small, iontophoretic injections of horseradish peroxidase conjugated to lectin throughout all major regions of the striatum (caudate-putamen, nucleus accumbens and olfactory tubercle). The results demonstrate that all major regions of the cerebral cortex project to the striatum on both sides of the brain with an ipsilateral predominance. The cells of origin of both the ipsilateral and contralateral corticostriate projections lie mainly in lamina V (especially lamina Va) with very small numbers in lamina III of the neocortex and mesocortex, and in the deep laminae of the allocortex. The results show that each striatal locus receives inputs from several cortical regions, i.e. there is extensive overlap in the corticostriate projection, and that, in general terms, each cortical region projects onto a longitudinally oriented region of the striatum. In particular, the major subdivisions of the cerebral cortex--the neocortex, mesocortex and allocortex--project onto defined but partially overlapping regions of the striatum: the neocortex projects to the caudate-putamen; the mesocortex projects mainly to the medial and ventral regions of the caudate-putamen but also to the ventral striatum (nucleus accumens and olfactory tubercle); and the allocortex projects mainly to the ventral striatum but also to the medial and ventral parts of the caudate-putamen. Within each of these major projection systems there is a further organization, with the constituent parts of each major cortical region projecting to smaller longitudinal components of the major projection fields. Each neocortical area projects to a longitudinal region of the dorsal striatum (caudate-putamen): the sensory and motor areas project topographically onto the dorsolateral striatum such that the rostral sensorimotor cortex (head areas) projects to central and ventral regions and the more caudal sensorimotor cortex (limb areas) projects to dorsal regions of the dorsolateral striatum; the visual area projects to the dorsomedial striatum; and the auditory area projects to the medial striatum. Each mesocortical area projects to a longitudinal area of the striatum: the most posteromedial mesocortex (the retrosplenial area) projects to the dorsomedial striatum; more anterior and lateral parts of the mesocortex project to more ventral parts of the striatum: and the most lateral mesocortex (the agranular insular and perirhinal areas) project to the ventrolateral striatum.(ABSTRACT TRUNCATED AT 400 WORDS)