LTP and spatial learning--where to next?

Hebb suggested, in 1949, that memories could be stored by forming associative connections between neurons if the criterion for increasing the connection strength between them be that they were active simultaneously. Much attention has been devoted towards trying to determine a) if there is a physiological substrate of such a rule, and b) if so, whether the phenomenon participates in real-life memory formation. The discovery of the electrically induced increase in synaptic strength known as long-term potentiation (LTP), in the early 1970s, demonstrated that a neural version of the Hebb rule could be observed under laboratory conditions in the hippocampus, a structure important for some types of learning. However, a quarter of a century later, the evidence linking LTP to learning and memory is still contradictory. The purpose of the present article is to review and assess the types of approach that have been taken in trying to determine whether hippocampal synaptic plasticity participates in memory formation.