From cortical plasticity to unawareness of visual field defects

It was long held that, following alterations in sensory input, structural c hanges in the primary visual cortex take place only in early life, during s o-called "critical periods." Recently, however, it has been established tha t, in adults, cortical maps in the brain are not fixed, and the cortex does not perform stereotyped operations. Instead, neuronal receptive fields in the cortex can reorganize following deactivation or an altered pattern of a ctivation. Plasticity is essential for the normal adjustment of the brain t o modifications in the sensory environment, and for improving perceptual sk ills and sensorimotor performances. It also plays a crucial role in recover y from damage to the visual system. Cortical remapping generates a filling- in of visual field defects. Consequently, it alters the image perceived. Co rtical rearrangement following lesions in the visual pathways does not rest ore function to the destroyed tissue, but it helps to compensate for gaps i n perception. In this review article, we focus on effects of plasticity in the adult visual cortex which are of major importance in the daily practice of neuro-ophthalmology. Cortical reorganization, together with resulting f illing-in, affects the early recognition and evaluation of visual field def ects. The importance of brain remapping in these matters is still largely u nderestimated by clinicians.