Anatomical and Physiological Basics

Whether you see the person you are in love with, try to listen to your own heartbeat, suffer from a headache, or crave for a chocolate cookie, one part of your brain is sure to increase its activity strongly: the insular cortex. The insular cortex, or 'insula' for short, is part of the cerebral cortex. J.C. Reil, a German neurologist, first named this brain structure in the early 19th century. Subsequent research findings have implicated the insula in an overwhelming variety of functions ranging from sensory processing to representing feelings and emotions, autonomical and motor control, risk prediction and decision-making, bodily- and self-awareness, and complex social functions like empathy. How is one single brain area involved in so many different tasks? Is the insula comprised of several functional regions? How are these related? And, are there any common themes underlying the apparently so heterogeneous roles of the insula?

Mental processes and their neural substrates are intimately linked to the homeostatic control of internal bodily state. There are a set of distinct interoceptive pathways that directly and indirectly influence brain functions. The anatomical organization of these pathways and the psychological/behavioral expressions of their influence appear along discrete, evolutionarily conserved dimensions that are tractable to a mechanistic understanding. Here, we review the role of these pathways as sources of biases to perception, cognition, emotion, and behavior and arguably the dynamic basis to the concept of self. Copyright © 2013 Elsevier Inc. All rights reserved.

Pleasant touch sensations may begin with neural coding in the periphery by specific afferents. We found that during soft brush stroking, low-threshold unmyelinated mechanoreceptors (C-tactile), but not myelinated afferents, responded most vigorously at intermediate brushing velocities (1-10 cm s(-1)), which were perceived by subjects as being the most pleasant. Our results indicate that C-tactile afferents constitute a privileged peripheral pathway for pleasant tactile stimulation that is likely to signal affiliative social body contact.