ABSTRACT
The concept that the hippocampus is “one of the most plastic structures in the brain” is reflected historically by two parallel lines of research; one anatomic and the other functional. The first demonstrations of anatomic plasticity revealed a remarkable degree of re-organization of neural connections due to sprouting in both developing and adult brains in hippocampus as well as related structures (Lynch et al., 1972; Raisman et al., 1966; Nadler et al., 1979; Steward et al., 1974). Made apparent by the newly located densities of synapses in adult brain and the convenience of laminated projections to easily demonstrate them, the hippocampus was exploited as a model anatomic system (Lynch et al., 1973, 1977). Thereafter, hippocampus rapidly became one of the primary “tools” for demonstrating anatomic and histochemical neuroplasticity, and still occupies a major role in that research arena (Hevroni et al. 1998). The almost simultaneous emergence of a second line of research unique to the hippocampus, was the demonstration of functional (synaptic) plasticity within a well defined hippocampal pathway in intact animals (Bliss and Lomo 1973; Lomo 1971a, b; Bliss and Gardner-Medwin 1973, Douglas and Goddard et al., 1975). Shortly thereafter demonstrations of synaptic potentiation and in particular “long-term potentiation” or “LTP” was reported in in vitro hippocampal preparations (Schwartzkroin and Wester 1975, Alger and Tyler 1976, Andersen et al., 1977, Gray and Johnston 1985) setting off a virtual explosion of studies in brain slices concerned with how hippocampal synapses are changed with “use” as defined by trains of electrical pulses delivered to afferent fiber tracts (Lynch 1986, Brown 1989, Muller et al., 1988, 1989; Malenka et al., 1986, 1988).
