INSULAR CORTEX AND NEIGHBORING FIELDS IN THE CAT - A REDEFINITION BASED ON CORTICAL MICROARCHITECTURE AND CONNECTIONS WITH THE THALAMUS

The insular areas of the cerebral cortex in carnivores remain vaguely defined and fragmentarily characterized. We have examined the cortical microarchitecture and thalamic connections of the insular region in c ats, as a part of a broader study aimed to clarify their subdivisions, functional affiliations, and eventual similarities with other mammals . We report that cortical areas, which resemble the insular fields of other mammals, are located in the cat's orbital gyrus and anterior rhi nal sulcus. Our data suggest four such areas: (a) a ''ventral agranula r insular area'' in the lower bank of the anterior rhinal sulcus, arch itectonically transitional between iso- and allocortex and sparsely co nnected to the thalamus, mainly with midline nuclei; (b) a ''dorsal ag ranular insular area'' in the upper bank of the anterior rhinal sulcus , linked to the mediodorsal, ventromedial, parafascicular and midline nuclei; (c) a ''dysgranular insular area'' in the anteroventral half o f the orbital gyrus, characterized by its connections with gustatory a nd viscerosensory portions of the ventroposterior complex and with the ventrolateral nucleus; and (d) a ''granular insular area'', dorsocaud al in the orbital gyrus, which is chiefly bound to spinothalamic-recip ient thalamic nuclei such as the posterior medial and the ventroposter ior inferior. Three further fields are situated caudally to the insula r areas. The anterior sylvian gyrus and dorsal lip of the pseudosylvia n sulcus, which we designate ''anterior sylvian area'', is connected t o the ventromedial, suprageniculate, and lateralis medialis nuclei. Th e fundus and ventral bank of the pseudosylvian sulcus, or ''parainsula r area'', is associated with caudal portions of the medial geniculate complex. The rostral part of the ventral bank of the anterior ectosylv ian sulcus, referred to as ''ventral anterior ectosylvian area'', is h eavily interconnected with the lateral posterior-pulvinar complex and the ventromedial nucleus. Present results reveal that these areas inte ract with a wide array of sensory, motor, and limbic thalamic nuclei. In addition, these data provide a consistent basis for comparisons wit h cortical fields in other mammals. (C) 1997 Wiley-Liss, Inc.