Insular cortex and neighboring fields in the cat: A redefinition based on cortical microarchitecture and connections with the thalamus

Abstract

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 cats, 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 rhinal sulcus. Our data suggest four such areas: (a) a "ventral agranular insular area" in the lower bank of the anterior rhinal sulcus, architectonically transitional between iso- and allocortex and sparsely connected to the thalamus, mainly with midline nuclei; (b) a "dorsal agranular 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 of the orbital gyrus, characterized by its connections with gustatory and viscerosensory portions of the ventroposterior complex and with the ventrolateral nucleus; and (d) a "granular insular area", dorsocaudal in the orbital gyrus, which is chiefly bound to spinothalamic-recipient thalamic nuclei such as the posterior medial and the ventroposterior inferior. Three further fields are situated caudally to the insular areas. The anterior sylvian gyrus and dorsal lip of the pseudosylvian sulcus, which we designate "anterior sylvian area", is connected to the ventromedial, suprageniculate, and lateralis medialis nuclei. The fundus and ventral bank of the pseudosylvian sulcus, or "parainsular area", is associated with caudal portions of the medial geniculate complex. The rostral part of the ventral bank of the anterior ectosylvian sulcus, referred to as "ventral anterior ectosylvian area", is heavily interconnected with the lateral posterior-pulvinar complex and the ventromedial nucleus. Present results reveal that these areas interact with a wide array of sensory, motor, and limbic thalamic nuclei. In addition, these data provide a consistent basis for comparisons with cortical fields in other mammals.

Connections of cat auditory cortex: II. Commissural system

“…1A,2K-L) and connectivity ( Fig. 9:ED, EI, EV) which imply that regional parcellation we chose is valid, and might lead to finer divisions as seen in other AC regions (Clascá et al, 1997(Clascá et al, ,2000. A further axis is suggested by the regionally specific laminar commissural origins, a pattern consistent with the idea that cortical areas embody multiple axes of representation and computation.…”

“…4, 9). Common sources of commissural input would not be predicted since In has predominantly limbic thalamic and amygdaloid relations (Clascá et al, 1997), whereas ED has mixed auditory and perivisual connections and no known limbic thalamic or cortical relation (Bowman and Olson, 1988a). Heterotopic convergence from these sources could explain the apparent physiological activation of an area by a broad array of commissural input , which can enable commissural integration of information across many cortical areas (Lee and Winer, 2008b).…”

Vagal Input to Lateral Area 3a in Cat Cortex

“…Even though the response was diffuse, there were two sites with larger response amplitude than neighbors: one in the anterior part of the lateral sigmoid gyrus and another more posterolaterally in the orbital gyrus. The former region is the subject of the present study, whereas the latter corresponds to the well-established "insular visceral sensory cortex" (Clasca et al 1997). Stimulation of either right or left vagus nerves elicited the evoked potential in the sigmoid gyrus.…”

Connections of cat auditory cortex: I. Thalamocortical system

“…It has vital roles in signal transformation (Creutzfeldt et al, 1980;Miller et al, 2001), attentional modulation (Steriade et al, 1998), and intracortical communication Guillery, 1996, 1998) that underscore its broad functional impact (Winer, 2006;Winer and Lee, 2007). Lemniscal and non-lemniscal nuclei within the MGB code (Winer and Morest, 1983) and carry streams of high fidelity (Miller et al, 2002), broadly tuned (Calford, 1983), multimodal (Bordi and LeDoux, 1994), and limbic (Clascá et al, 1997) information to primary and non-primary auditory areas, respectively (Andersen et al, 1980). How many such areas exist and their relation with MGB subdivisions is unknown, and is the subject of this study.…”