Organization of visceral and limbic connections in the insular cortex of the rat

Abstract

The anterograde and retrograde transport of horseradish peroxidase was used to study the anatomical organization of visceral and limbic terminal fields in the insular cortex. Following injections into the ventroposterolateral parvicellular (VPLpc) and ventroposteromedial parvicellular (VPMpc) visceral relay nuclei of the thalamus, dense anterograde and retrograde labeling was present in the posterior granular and dysgranular insular cortices, respectively. The parabrachial nucleus had extensive connections with the posterior dysgranular cortex and to a lesser degree with the anterior dysgranular and granular cortices. In contrast, injections into the medial prefrontal cortex and mediodorsal nucleus of the thalamus resulted in dense anterograde and retrograde labeling primarily in the anterior agranular cortex, whereas injections in the amygdala resulted in axonal labeling in the agranular and dysgranular insular cortices. Injections into the lateral hypothalamic area resulted in dense anterograde and retrograde labeling mainly in the agranular and dysgranular cortices and moderate to light labeling in the granular cortex. Our results indicate that ascending visceral afferents, VPLpc, VPMpc, and parabrachial nuclei, are topographically organized in the granular and dysgranular fields of the insular cortex, whereas the agranular cortex appears to receive highly integrated limbic afferents from the infralimbic cortex and the mediodorsal nucleus of the thalamus. Although these visceral and limbic inputs to the insular cortex are segregated for the most part into different longitudinally oriented strips of cortex, limbic input from the lateral hypothalamic area and the amygdala, which have extensive autonomic as well as limbic connections, are more diffusely distributed over the different regions of the insular cortex. This organization may subserve a role for the insular cortex in integration of autonomic response with ongoing behaviour and emotion.

Rat brains also have a default mode network

“…Notably, it does not include IL, an important region within the medial network, nor does it include the insular orbital network structures [AIv, DI, and GI]. However, insular cortex sends projections to OMPFC, in particular LO, VLO, PrL, and IL (31,32), and thus, through corticocortical connections (32,33), highly integrated viscerosensory information reaches the medial and orbital networks of OMPFC.…”

Neural correlates of a ‘pessimistic’ attitude when anticipating events of unknown emotional valence

“…The ventromedial thalamus is considered to be a relay within the visceroceptive pathway to posterior and anterior insula (Craig, 2002). The centromedial thalamus projects to the ACC, insula, and amygdala (Augustine, 1996;Collins and Pare, 1999;Vogt, 2005;Minamimoto et al, 2005), the dorsomedial thalamus, as well to the insula and the ACC, both supposedly for emotional-motivational functions (Heimer, 2003;Allen et al, 1991).…”

“…Insular regions have a wide range of reciprocal connections to prefrontal areas, ACC, thalamus, amygdala, hypothalamus, and to brainstem regions as the parabrachial nucleus for relaying visceral afferents (Augustine, 1996;Yasui et al, 1991). Furthermore, the insula receives input from the aforementioned medial thalamic regions (Augustine, 1996;Allen et al, 1991). On the functional level, the insula was found to be involved in the anticipation of electric shocks (Chua et al, 1999), noxious thermal stimuli (Ploghaus et al, 1999), fear indicating stimuli together with the amygdala (Phelps et al, 2001), and of aversive pictures (Simmons et al, 2004).…”

The Insular Cortex and the Amygdala: Shared Functions and Interactions

“…The gustatory area within the IC is localized in the dysgranular insular cortex [21,29], roughly between the rhinal fissure and the medial cerebral artery (MCA) -an area that has also been identified in the rat as taste-responsive using intrinsic signal imaging [141] and electrophysiological recordings [7,28,69,140,[142][143][144].…”

“…The Insular Cortex and the Amygdala: Shared Functions and Interactions 239 between the insular cortex and the amygdala [10,23,29,177,178] to all amygdalar subdivisions [179]. The ventral agranular insular area projects preferentially to the medial extended amygdala, while the viscerosensory and somatosensory portions of the insular cortex project preferentially to the central extended amygdala [180].…”