I have been studying a form of physiological synaptic plasticity in the hippocampus that is a promising candidate substrate mechanism for rapid associative conditioning. This activity-dependent phenomenon--which I term associative long-term potentiation (LTP)--has the following interesting features: (a) it can be induced rapidly; (b) it is extremely persistent; (c) it is specific to those synapses in which the activity has occurred; (d) it may be induced in an associative manner; (e) the associative induction of the modification adheres to strict timing requirements; and (f) it may be induced differentially. I will continue to examine the bioiphysical mechanisms involved in the associative induction steps, and continue to add to the list of known properties. Using brain slices taken from hippocampus, I plan to apply in vitro neurophysiological techniques and paradigms to provide evidence about the possible role as a substrate for the rapid-learning memory system, in which the hippocampus is thought to participate. I shall examine synaptic parallels to second-order conditioning, blocking, extinction and fogetting. I will also begin to isolate the key causal neurophysiologcal events that associatively induce the synaptic modification. The results should bear directly on our understanding of the neurophysiology of memory and indirectly on various neurological disorders that affect memory.