We present a comprehensive analysis of the cortical connections of the insu
lar and adjacent cortical areas in the domestic cat by using microinjection
s of wheat-germ agglutinin conjugated to horseradish peroxidase. We examine
d the identity and extent of the cortical fields connected to each area, th
e relative anatomical weights of the various connections, their laminar ori
gin, and their paths across the cerebral commissures, Our main finding is t
hat despite their relatively small size and close apposition, the connectio
ns of the insular and adjacent areas are far more widespread and more speci
fic to each area than previously realized, suggesting that each area is inv
olved in disparate aspects of cortical integration. The granular insular ar
ea is linked to a constellation of somatosensory, motor, premotor and prefr
ontal districts. The dysgranular insular area is chiefly associated with la
teral prefrontal and promotor, lateral somatosensory and perirhinal cortice
s. The dorsal agranular insular area is connected with limbic neocortical f
ields, while the ventral agranular insular area is associated with an array
of olfactory allocortical fields. The anterior sylvian area is associated
with visual, auditory and multimodal areas, with the dorsolateral prefronta
l cortex, and with perirhinal area 36. The parainsular area is linked to no
n-tonotopic auditory and ventromedial frontal areas. Trajectories followed
by the callosal axons of each of the investigated areas are extremely diver
gent. As a whole, the picture of the insular region that emerges from this
and a parallel study (Clasca et al., J Comp Neurol 384:456-482, 1997) is th
at of an extreme heterogeneity, both in terms of histological architecture
and neural connections. Comparison with earlier published reports on primat
es suggests that most, but not all, of the areas we investigated in cats ma
y have an direct counterpart within the insula of Old World monkeys.