ABSTRACT
Long-term potentiation (LTP) is defined as an enduring alteration in synaptic efficacy or gain following repeated afferent activation (Figure 9.1). LTP is usually considered an NMDA receptor-dependent mechanism underlying memory storage in the brain and is usually studied in brain areas closely associated with the storage of behavioral memory, for example, the hippocampal formation and, to a lesser extent, cerebral neocortex. While this is a reasonable operational definition of the features of LTP, it provides a limited view regarding the biological function of this form of synaptic alteration. The reason that LTP is favored as a neural system underlying memory storage is due to its unique phenomenology. Almost alone among those functional changes known to exist in the brain, LTP has the induction characteristics and longevity necessary to place it firmly as a candidate for the storage of experiential memory in the brain. That is, LTP is induced only by sufficient levels of afferent activity, it displays an induction threshold, and it can be induced in an associative fashion such that a strong and weak input when active together will result in LTP at the weak input (which normally would not induce LTP). Associativity is a feature close to the hearts of learning theorists, who view the association of a strong and weak stimulus as an important associative consideration in the establishment of cognitive memory (Teyler & DiScenna, 1987).
