Insula connections with the parieto-frontal circuit for generating arm actions in humans and macaque monkeys

It has been recently found that the human dorso-central insular cortex contributes to the execution and recognition of the affective component of hand actions, most likely through modulation of the activity of the parieto-frontal circuits. While the anatomical connections between the hand representation of the insula and, the parietal and frontal regions controlling reaching/grasping actions is well assessed in the monkey, it is unknown the existence of a homolog circuit in humans. In the present study, we performed a multifiber tractography investigation to trace the tracts possibly connecting the insula to the parieto-frontal circuits by locating seeds in the parietal, premotor, and prefrontal nodes of the reaching/grasping network, in both humans and monkeys. Results showed that, in both species, the insula is connected with the cortical action execution/recognition circuit by similar white matter tracts, running in parallel to the third branch of the superior longitudinal fasciculus and the anterior segment of the arcuate fasciculus.