Brain Commissural Anomalies

The human brain commissures include the corpus callosum (neocortical), the anterior commissure (paleocortical), the fornix (archicortical) [ the hippocampal commissure (also called commissure of psalterium Davidi or David’s lyre in the older literature)] (Raybaud, 2010) and the posterior commisure (Keene, 1938). The largest of the commissures in advanced mammals is the corpus callosum that holds its name from its compactness (Raybaud, 2010) which develops embryologically in intimate relationship to the hippocampal formation, fornix, septum pellucidum, and cingulate gyrus (Swayze et al., 1990). It has already been accepted that the commissural fibers are important for transfer of complex cognitive information between the brain hemispheres (Zaidel, 1994; van der Knaap & van der Ham, 2011) and coordinated transfer of information is essential for the cerebral functions (Moldrich et al., 2010). In normal condition, commissural fibers must be actively guided across the midline to reach their targets in the contralateral hemisphere. When the underlying mechanisms regulating the guidance of commissural fibers fail, pathological dysgenesis of one or more commissures ensues. It is suggested that a complex set of cellular and molecular mechanisms regulate commissural development (Ren et al., 2006). Malformation of the corpus callosum is a various condition, which can be observed either as isolated form or as one manifestation in the context of congenital syndromes (Schell-Apacik et al., 2008). Based on survey of 596 network families, the most frequently clinical findings reported about agenesis of the corpus callosum are developmental delay, visual problems, language delay, seizures, and muscletone issues (Schilmoeller & Schilmoeller, 2000). Furthermore, agenesis of the corpus callosum results in disabilities in social cognition that appears to be secondary to deficits in complex cognitive operations such as reasoning, concept formation, and problem solving (Doherty et al., 2006). Also, there is no evidence that individuals with partial agenesis of the corpus callosum have better outcomes than individuals with complete agenesis the corpus callosum (Moes et al., 2009). Although, the embryology, anatomy, functions, anomalies and molecular mechanisms of the human brain commissures have been extensively studied over the past years. However a need to an overall and new collection on the basis of the other recent studies was seriously felt. Therefore this chapter is to provide a collection of the fundamental principles of the embryogenesis, organization, congenital malformations of brain commissures. The chapter presents new information about prevalence, the brain disorders associated with commissural anomalies, the etiology and the pathogenetic mechanisms that have been understood in recent years in this issue in the neurosciences.