The visual cortex has been a model for plasticity in the nervous system ever since the pioneering work of Wiesel and Hubel (1963). It is a model for neural plasticity at the synaptic level, the best illustration of the nature-nurture controversy about the development of the nervous system, and the best example of the mechanisms that underlie clinical deficits in development. In particular, monocular deprivation, produced by closing the eyelids of one eye, which corresponds to unilateral cataract in the human, has significant physiological and anatomical results. These underlie the resulting amblyopia (poor vision which has no obvious cause in the retina) that can amount to total unilateral blindness in severe cases. Thus, the anatomy and physiology can be correlated with behavioral consequences by studying the visual system.

Many forms of plasticity have been studied in the visual cortex. While the physiology has been studied in most forms and the anatomy in many, most experiments concerned with biochemical mechanisms have been done on three: ocular dominance plasticity, orientation and direction plasticity, and long-term potentiation and long-term depression. These are the three forms that will be discussed in this chapter.

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