Synaptic Plasticity

Activity-dependent synaptic plasticity has been implicated as the basic mechanism underlying learning and memory. In 1949, Hebb posited a theory explaining this phenomenon of synaptic plasticity. He proposed that prolonged changes in neural circuitry occurred in response to the combined activation of two cell systems, such that "any two cells that are repeatedly active at the same time will tend to become 'associated,' so that activity in one facilitates activity in the other." Subsequent studies in the 1960s and 1970s led to the discovery that repeated activation of presynaptic neurons at certain frequencies resulted in an extended alteration in the postsynaptic response. The phrase "long-term potentiation" was coined by Bliss and Lomo in 1973, following a study in which they systematically analyzed this form of synaptic plasticity in rabbit hippocampal brain slices in terms of prolonged changes in EPSP amplitude and the firing patterns of postsynaptic cells. Taken from this study, the figure on the right illustrates how application of a stimulus train consisting of 15 pulses/s for 10 s in the perforant pathway results in LTP in the dentate area. Unknown macro: {align} LTP of the perforant path-dentate synapse.