Long-term potentiation (LTP) of synaptic efficacy following repetitive (tetanic) inputs was described originally in the hippocampus, and it has been studied extensively based on the hypothesis that it represents a synaptic model for learning and memory in the brain. In the developing visual cortex, long-term depression (LTD) as well as LTP was found to be induced by tetanic stimulation of afferents, and such a synaptic modification was proposed as a basis for experience-dependent change in functional properties of cortical neurons during the critical period of postnatal development. This chapter deals with the induction of LTP and LTD in visual cortex and their possible functional significances. Among possible molecular mechanisms for the induction of LTP and LTD, those including the involvement of NMDA receptors, Ca2+/calmodulin dependent protein kinase II, protein kinase C, phosphatidylinositol turnover and membrane-associated cytoskeletal proteins have been reviewed, although the results obtained so far in visual cortex are only fragmentary.
