The temporal dynamics of retention of a context memory: something is missing.
We use a variation of contextual fear conditioning, called the context pre-exposure facilitation effect (CPFE) to study the rat's memory for context. In this paradigm, the rat is pre-exposed to a conditioning context and later returned to that context, where it is immediately shocked. The memory context is revealed by the fact that pre-exposure to the conditioning context, but not to a different context, greatly enhances conditioned fear produced by immediate shock. We report that rat's retention of the context memory is a nonmonotonic U-shaped function of the interval separating pre-exposure and immediate shock. Retention performance decays rapidly so that within 2 min of pre-exposure there is no evidence that the rat was pre-exposed to the context. Within a few hours, however, a strong CPFE was observed that persisted for at least 28 d. Two hypotheses are discussed: (1) the descending arm of the U represents a retrieval failure, and (2) the U-shaped function represents two discontinuous memory processes initiated in parallel-short-term synaptic changes that are rapidly initiated, but also decay rapidly, and long-term synaptic processes that take time to generate but can endure for days.
Rudy
Jerry W
JW
Department of Psychology, Center for Neuroscience, University of Colorado, Boulder, Colorado 80309, USA. JRudy@Clipr.Colorado.Edu
Wright-Hardesty
Karli
K
D000818:Animals; D001245:Association Learning / Q000502:physiology*; D003214:Conditioning, Classical / Q000502:physiology*; D004777:Environment; D005239:Fear / Q000502:physiology*; D008297:Male; D051381:Rats; D020318:Rats, Long-Evans; D012153:Retention, Psychology / Q000502:physiology*; D013997:Time Factors