How is new information organized in memory? According to latent state theories, this is determined by the level of surprise, or prediction error, generated by the new information: small prediction error = updating of existing memory, large prediction error = encoding of new memory. We tested this idea using a protocol in which rats were first conditioned to fear a stimulus paired with shock. The stimulus was then gradually extinguished by progressively reducing the shock intensity until the stimulus was presented alone. Consistent with latent state theories, this gradual extinction protocol (small prediction errors) was better than standard extinction (large prediction errors) in producing long-term suppression of fear responses, and the benefit of gradual extinction was due to updating of the conditioning memory with information about extinction. Thus, prediction error determines how new information is organized in memory, and latent state theories adequately describe the ways in which this occurs.Nicholas G. W. Kennedy, Jessica C. Lee, Simon Killcross, Fred Westbrook, Nathan M. HolmesbioRxiv 2024.01.16.575867; doi: https://doi.org/10.1101/2024.01.16.575867
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The data from conditioning, the common extinction session, the spontaneous recovery and 548 reinstatement tests were analyzed using a set of planned orthogonal contrasts (Hays, 1967)(Hays, 1967). 549 Data from the gradual extinction and extinction sessions (days 4-6) were analyzed using a mixed-model 550 ANOVA with a between factor of Group and a within factor of Day. The type one error rate was controlled 551 at = 0.05 which gave an F critical of 4.600 (df 1 and 14) for extinction training and 4.325 for all other 552 stages (1 and 21 df). The first of the planned contrasts compared Groups Extinction and Gradual Extinction 553 to Group Single Extinction to assess whether the treatments accorded the former groups had produced a 554 greater long-term depressive effect on conditioned responding than the latter, i.e., the group just given the 555 single extinction session. The second contrast compared Group Gradual Extinction to Group Extinction to 556
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558 Experiment 3 559 Subjects, apparatus and stimuli 560 The subjects were 12 male and 12 female experimentally nave rats of the same age, from the same 561 source and maintained under the same conditions described previously. The apparatus and stimuli were 562 those used previously 563
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Procedure 564 Context Exposure and Conditioning. On days 1-3, all rats received context exposure and 565 conditioning in the manner described in Experiment 1. 566 Extinction Stage 1. Rats were randomly allocated to three groups (n = 8). On each of days 4-6, rats in 567 groups extinction and gradual extinction received tone alone presentations and progressive reductions in 568 shock intensity, respectively, in the manner described in Experiment 1. On each of these days, Rats in Group 569 Scrambled continued to receive pairings of the tone and shock. The number and intensity of the pairings 570 matched those administered Group Gradual Extinction, but were arranged in a pseudo-random order. The 571 order is as follows: Day 1 = 0.4, 0.1, 0.2, 0.2, 0.4, 0.1, 0.4, 0.2 mA; Day 2 = 0.2, 0.1, 0.4, 0.1, 0.4, 0.2, 0.1; 572 Day 3 = 0.1, 0.4, 0.2, 0.4, 0.1, 0.1, 0.4, 0.2. All subjects within the group received the same sequence. 573
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