Elsevier

Neuroscience

Volume 8, Issue 4, April 1983, Pages 791-797
Neuroscience

Temporal contiguity requirements for long-term associative potentiation/depression in the hippocampus

https://doi.org/10.1016/0306-4522(83)90010-6Get rights and content

Abstract

A previous study utilizing the powerful ipsilateral and weak crossed projection from the entorhinal cortex to the dentate gyrus in the rat revealed that long-term potentiation is an associative process in these systems. If the weak crossed projection alone receives potentiating stimulation consisting of 8 high-frequency trains 17.5 ms in duration, it does not exhibit long-term potentiation. However, long-term potentiation can be induced in the crossed projection if it is activated concurrently with the converging ipsilateral system. The present study is designed to determine the degree of synchrony required for the associative interactions by varying the timing and order of the potentiating trains delivered to the two converging systems.

The associative induction of long-term potentiation does not require perfectly synchronous activation of the converging systems. The order of the trains is crucial, however. Long-term potentiation of the crossed projection can be induced if activity in the ipsilateral system is concurrent with or follows activity in the crossed projection. Indeed, there can be as much as 20ms between the 17.5ms trains in the two systems, and long-term potentiation of the crossed projection is still induced. Activation of the ipsilateral system that precedes activation of the crossed system depresses the responses evoked by the crossed system. If potentiating stimulation of the ipsilateral system follows activation of the crossed projection by too long an interval (200 ms, for example), then the crossed projection is depressed rather than potentiated.

These results are discussed with regard to the nature of the associative process permissive for the induction of long-term potentiation and lead us to the conclusion that perfect temporal contiguity is not a requirement of this prototypical elemental memory unit.

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