<P> Timothy Bliss, who joined the Andersen laboratory in 1968, collaborated with Lømo and in 1973 the two published the first characterization of long - lasting potentiation in the rabbit hippocampus . Bliss and Tony Gardner - Medwin published a similar report of long - lasting potentiation in the awake animal which appeared in the same issue as the Bliss and Lømo report . In 1975, Douglas and Goddard proposed "long - term potentiation" as a new name for the phenomenon of long - lasting potentiation . Andersen suggested that the authors chose "long - term potentiation" perhaps because of its easily pronounced acronym, "LTP". </P> <P> The physical and biological mechanism of LTP is still not understood, but some successful models have been developed. (1) Studies of dendritic spines, protruding structures on dendrites that physically grow and retract over the course of minutes or hours, have suggested a relationship between the electrical resistance of the spine and the effective synapse strength, due to their relationship with intracellular calcium transients . Mathematical models such as BCM Theory, which depends also on intracellular calcium in relation to NMDA receptor voltage gates, have been developed since the 1980s and modify the traditional a priori Hebbian learning model with both biological and experimental justification . Still others have proposed re-arranging or synchronizing the relationship between receptor regulation, LTP, and synaptic strength . </P> <P> Since its original discovery in the rabbit hippocampus, LTP has been observed in a variety of other neural structures, including the cerebral cortex, cerebellum, amygdala, and many others . Robert Malenka, a prominent LTP researcher, has suggested that LTP may even occur at all excitatory synapses in the mammalian brain . </P> <P> Different areas of the brain exhibit different forms of LTP . The specific type of LTP exhibited between neurons depends on a number of factors . One such factor is the age of the organism when LTP is observed . For example, the molecular mechanisms of LTP in the immature hippocampus differ from those mechanisms that underlie LTP of the adult hippocampus . The signalling pathways used by a particular cell also contribute to the specific type of LTP present . For example, some types of hippocampal LTP depend on the NMDA receptor, others may depend upon the metabotropic glutamate receptor (mGluR), while still others depend upon another molecule altogether . The variety of signaling pathways that contribute to LTP and the wide distribution of these various pathways in the brain are reasons that the type of LTP exhibited between neurons depends in part upon the anatomic location in which LTP is observed . For example, LTP in the Schaffer collateral pathway of the hippocampus is NMDA receptor - dependent, whereas LTP in the mossy fiber pathway is NMDA receptor - independent . </P>

Which of the following hippocampal techniques enhanced the study of ltp and ltd