Abstract We approach the functional significance of extra-relay afferents to primary sensory areas by searching for rules governing their distribution upon the cortical spaces of single representations. We address the question whether the input from a single extra-relay structure is distributed evenly or unevenly within the space of a single cortical area. Projections from the thalamic anterior intralaminar nuclei and from the claustrum to the primary somatosensory and visual cortices are analyzed and compared with those from the thalamic relay nuclei. Our analysis demonstrates that extra-relay projections change along with the representation within the same primary sensory cortex. Functional implications of this finding are discussed.