Thalamic connections of the insula in the rhesus monkey and comments on the paralimbic connectivity of the medial pulvinar nucleus

Abstract

Thalamic connections of the insula in the rhesus monkey were studied with axonal transport methods. Tritiated amino acid injections limited to the insula revealed autoradiographic label in the principal and parvicellular components of the ventroposterior medial nucleus, the ventroposterior inferior nucleus, the oral and medial pulvinar nuclei, the nucleus reuniens, the parvicellular and magnocellular components of the medial dorsal nucleus, the centromedian-parafasicularis nuclei, and the reticular nucleus. In additional animals, tritiated amino acids and horseradish perioxidase injections were made within different regions of the insula. Although the injection sites in these additional cases may have included minor extensions into claustrum and adjacent structures, several tentative conclusions emerged with respect to the antero-posterior gradient in insulothalamic connectivity. The anterior insula appears to have a more extensive relationship with the ventroposterior medial complex, the medial dorsal nucleus, the centromedian-parafasicularis nuclei and with some midline nuclei. In contrast, the posterior insula is more extensively connected with the ventroposterior inferior nucleus, the oral and medial pulvinar nuclei, and the suprageniculate nucleus. The patterns of insulothalamic connections support conclusions derived from observations on the cortical connectivity of the primate insular cortex indicating that the anterior insula is related to olfactory, gustatory, and viscero-autonomic behavior, whereas the posterior insula is related to auditory-somesthetic-skeletomotor function (Mesulam and Mufson, '82b). The medial pulvinar nucleus has extensive connections with many paralimbic cortical regions including the insula as well as with high order polymodal association cortex. These findings suggest that the medial pulvinar may provide a region for the convergence of multisensory association input with limbic information.