Novel Insights from Fourier-Transform InfraRed Imaging on the Morpho-Chemical Profile of Human Corpus Callosum  
[PERSON]  
1 Department of Life and Environmental Sciences, Polytechnic University of Marche, 60131 Anconca, Italy 11 Department of Legal Medicine, Azienda Ospedaliero-Universitaria Ospedali Riuniti, 60020 Anconca, Italy 11 Department of Electrical and Clinical Medicine, Polytechnic University of Marche, 60020 Anconca, Italy 11 Department of Biomedical Science and Public Health, Polytechnic University of Marche, 60020 Anconca, Italy 11 Department of Life and Environmental Sciences, Polytechnic University of Marche, 60131 Anconca, Italy 11 Department of Electrical and Clinical Medicine, Polytechnic University of Marche, 60020 Anconca, Italy 11 Department of Electrical and Clinical Medicine, Polytechnic University of  
insulating lipidic layers of membrane wrapped around axons by oligodendrocytes (ODCs), is essential for normal impulse conduction. The myelin sheath is composed mainly of lipid (phospholipid, glycolipid and cholesterol; 70 to 85%) and a low proportion of protein (15 to 30%) [15]. Myelin production is regulated by a category of ODCs precursor cells that fire action potentials and dynamically interact with electrical impulse transmission in neural circuits [10]. The human CC is divided into five anatomical regions, which comprise, from front to back, the genu, body or trunk (subdivided into anterior, middle, and posterior body), isthmus, and splenium [16]. Several methods, principally based on geometric criteria, have been proposed and exploited to define these subregions, given the lack of clear edges between them [16; 17; 18; 19]. These callosal regions display different fiber compositions: fibers with a large diameter have been identified in the posterior part of the splenium and in the body, regions known to contain interhemispheric sensory fibers that cross the commissure and exchange information at high speed; on the other hand, smaller fibers, mainly connecting associated cortical areas, have been described in the rostrum, genu, and anterior body [20; 21]. Accordingly, a different myelination is reported: in vitro (histological) and in vivo (functional) analyses evidenced a higher amount of myelin in the posterior splenium and posterior body [22; 23]. The difference in composition is also related to different functions, as evidenced in patients who have undergone surgical resection of the posterior or anterior part of the CC. The process of fiber myelination becomes significant at about 6 months of postnatal life in the splenium and at around 8 months in the genu. Myelination proceeds from posterior to anterior [24; 25], consistently with the known mechanism through which myelination of primary cortical areas (somatic sensory, motor, auditory, visual), connected through the isthmus and splenium, precedes the myelination of the body, genu, and rostrum, connecting the more anterior associative areas. Myelination is faster during childhood and adolescence and continues slowly during middle age. Moreover, besides the variation in myelin content, maturation and aging are also characterized by deep changes in the caliber and density of myelinated and unmyelinated axons, with structural degradation of myelin sheaths typical of advanced age [26]. Recently, different profiles of protein expression have also been described in the three main CC regions (genu, body, and splenium). In particular, the expression of proteins related to antioxidant activity and glucose metabolism was shown to be higher in the splenium compared with the genu and body [27]. During aging, the CC is subject to a physiological loss of myelin content, which is more pronounced and occurs earlier in the anterior regions than in posterior [28]. Among the many analytical techniques available, Fourier-transform infrared imaging (FTIRI) spectroscopy is a powerful and label-free vibrational tool, extensively applied to analyze the biomolecular composition and building of cells and tissues [29; 30; 31; 32].