Development of the human fetal insular cortex: study of the gyration from 13 to 28 gestational weeks

Abstract

To describe the morphological stages of insular sulci and gyri development we carried out a macroscopical study on 21 human fetal brains, showing no anomalies, from 13 to 28 gestational weeks (GWs). Particular focus was given to morphological appearance during the development of insular and periinsular structures, especially the gyration and sulcation of the insula, central cerebral region and opercula, as well as the vascularization of these regions. The periinsular sulci and the central (insular and cerebral) sulci were the first macroscopical structures identified on the lateral surface of the human fetal cerebral hemisphere with earlier development on the right hemisphere. Here we describe five stages of insular gyral and sulcal development closely related to gestational age: stage 1: appearance of the first sulcus at 13-17 GWs, stage 2: development of the periinsular sulci at 18-19 GWs, stage 3: central sulci and opercularization of the insula at 20-22 GWs, stage 4: covering of the posterior insula at 24-26 GWs, stage 5: closure of the sylvian fissure at 27-28 GWs. We provide evidence that cortical maturation (sulcation and gyration) and vascularization of the lateral surface of the brain starts with the insular region, suggesting that this region is a central area of cortical development.

MRI-Based Definition of a Stereotactic Two-Dimensional Template of the Human Insula

“…These two sulci have two different axes separated by a clear angle (mean angle 126°). Interestingly, an embryology study shows the inferior sulcus becoming visible earlier than the posterior one, appearing at the 13th week as compared to the 17th week of gestation [53] .…”

“…This may be due to the following reasons: (i) in the fetus, the inferior and posterior peri-insular sulci and the CIS develop first [53] , which gives them greater developmental and positional stability. (ii) Fetal development of the human brain shows that the temporoparietal operculum progresses around the posterior insula earlier than around the anterior insula.…”

“…This closes the posterior aspect of the sylvian fissure before its anterior part. So, this opercularization process stops the extension of the posterior insular subdivision and the displacement of its sulci at the first stages of the fetal development [53] . (4) The two-dimensional template of the insula is simple and reproducible.…”

Aberrant cortical gyrification in schizophrenia: a surface-based morphometry study

“…46 This is supported by the observation that the insula is one of the earliest brain structures to show gyrification and neuronal differentiation and thus forms a core zone of sulcal and gyral maturation during normal intrauterine growth. 47 Most of the other regions showing hypogyria in patients with schizophrenia (inferior frontal, superior temporal and inferior parietal regions) belong to the multimodal (heteromodal) association cortex described by Mesulam. 48 A pathological perturbation in the development of multimodal association areas has been previously suggested as the core deficit in patients with schizophrenia.…”

Does the salience network play a cardinal role in psychosis? An emerging hypothesis of insular dysfunction

“…Evidence from studies of human fetal brains suggests that the process of development of cortic al folding (gyrification) is first notable in the insular region and proceeds in an orderly fashion. 33 The peri-insular sulci and the central (insular and cerebral) sulci are the first macroscopic structures visible on the lateral surface of the human fetal cerebral hemisphere; they can first be seen between gestational weeks 13-17. This is a crucial period for neuronal migration that is considered to be important in the etiology of schizophrenia.…”