The organization of the claustroneocortical projections in the cat studied by means of the HRP retrograde axonal transport.

The projections from the claustrum to the cerebral cortex were examined in the cat by means of horseradish peroxidase (HRP) injections in various different areas of the lateral and medial surfaces of the neocortex. In all cases retrogradely labeled cells were observed in the ipsilateral claustrum insulare (ClI). In most of the cases some labeled cells were also observed in the contralateral ClI. The number of labeled cells was higher following large HRP injections in some cortical areas, such as the motor and visual cortex, than following large HRP injections in other areas, such as the second somatic sensory cortex. The patterns of distribution of labeled cells in the ClI following the different HRP injections evidenced a prevalent anteroposterior and dorsoventral topographical arrangement. However, some degree of overlapping was evident in the distribution of cells retrogradely labeled from injections in different cortical fields. The results of the present study indicate that: a) in all likelihood the claustral projections are distributed upon the entire neocortex; b) they are not uniformly distributed upon the neocortex from the quantitative point of view; c) the arrangement of the claustrocortical projections is predominantly but not strictly topographical. The widespread distribution of the claustral inputs suggests that they must be integrated in different models of cortical activity.