21 - Development of visual callosal connections

Summary

A prominent characteristic of the connections between cortical sensory areas is the close relationship that the overall pattern of these connections bears to the orderly representations of the sensory periphery that are a ubiquitous feature of these cortical areas. This relationship holds true not only for projections that arise and terminate within the same cerebral hemisphere, but also for the extensive system of interhemispheric cortico-cortical connections. For example, the topography of the interhemispheric pathway between cortical visual areas is such that the highest density of these connections is commonly found wherever the vertical meridian of the visual field is represented.

Although a great deal is known about the arrangement of visual cortico-cortical connections in the adult, our knowledge of the process by which this intricate pattern of connections is specified during development is much less complete. No doubt this is due at least in part to the abundant numbers and highly interwoven nature of the afferent and efferent cortical pathways, which makes it difficult to manipulate and study the development of any one set of projections in isolation. However, the interhemispheric visual cortico-cortical connections have a unique trajectory that carries them through the corpus callosum, a broad fiber tract that is visible in the interhemispheric fissure from an early stage of development onward. For this reason, much of what we know about the development of visual cortico-cortical connections comes from studies of the visual callosal pathway.