From the lateral edge to the center of the cortex: The development of the human insula

Abstract

Abstract The human insula is a key node in a neuronal network which integrates interoceptive stimuli from the own body, and exteroceptive stimuli from the environment, and thus maintains the autonomic, emotional and socio-cognitive homeostasis of the body. In the last years, the insula has come into the focus of attention. Comparative anatomical studies showed that in many species the insula forms the lateral edge of the cortex. Very little is known about the prenatal development of the human insula, which is the first cortical region to mature. The origin of the pyramidal neurons for the insula is a small sector of the proliferating ventricular/subventricular zone at the cortico-striatal boundary (CSB). The CSB contains the radial glia cells, which are stem cells and give rise to a dense fascicle of radial glia processes. This fascicle traverses the external capsule and serves as a migration substrate for the neuroblasts on their way from the CSB into the insula. Around the 10/11th week of gestation, the lateral ventricle and its adjacent structures including the CSB bend in a C-shaped fashion. The insula now develops between a dorsal, fronto-parietal and a ventral, temporal CSB, which provide descending and ascending streams of neuroblasts, respectively, migrating along the radial glia fascicle. As a consequence of the ventricular rotation during ontogenesis, the human insula changes its initial position at the lateral edge of the cortex to its final central location, which reflects its integrative functions in brain activity.