Abstract
Previous research indicates that extinction of rodent maze behavior may occur without explicit performance of the previously acquired response. In latent extinction, confining an animal to a previously rewarded goal location without reinforcement is typically sufficient to produce extinction of maze learning. However, previous studies have not determined whether latent extinction may be successfully employed to extinguish all types of memory acquired in the maze, or whether only specific types of memory may be vulnerable to latent extinction. The present study examined whether latent extinction may be effective across two plus-maze tasks that depend on anatomically distinct neural systems. Adult male Long-Evans rats were trained in a hippocampus-dependent place learning task (Experiment 1), in which animals were trained to approach a consistent spatial location for food reward. A separate group of rats were trained in a dorsolateral striatum-dependent response learning task (Experiment 2), in which animals were trained to make a consistent egocentric body-turn response for food reward. Following training, animals received response extinction or latent extinction. For response extinction, animals were given the opportunity to execute the original running approach response toward the empty food cup. For latent extinction, animals were confined to the original goal locations with the empty food cup, thus preventing them from making the original running approach response. Results indicate that, relative to no extinction, latent extinction was effective at extinguishing memory in the place learning task, but remained ineffective in the response learning task. In contrast, typical response extinction remained very effective at extinguishing memory in both place and response learning tasks. The present findings confirm that extinction of maze learning may occur with or without overt performance of the previously acquired response, but that the effectiveness of latent extinction may depend on the type of memory being extinguished. The findings suggest that behavioral treatments modeled after response extinction protocols may be especially useful in alleviating human psychopathologies involving striatum-dependent memory processes (e.g., drug addiction and relapse).
Highlights
Mammalian memory is not a unitary phenomenon, but rather it transpires through distinct systems
A variety of memory systems have been dissociated in the mammalian brain (Squire, 2004; White et al, 2013), significant attention has been devoted to anatomical dissociations between a spatial/cognitive memory system mediated by the hippocampus and a stimulus-response (S-R)/habit system mediated by the dorsolateral striatum (DLS; Packard et al, 1989; Packard and McGaugh, 1992, 1996; McDonald and White, 1993; Packard and Teather, 1997; Chang and Gold, 2003; Iaria et al, 2003; Compton, 2004)
A 3 × 8 ANOVA (Group × Day) computed on latency (Figure 1B) indicated a significant effect of Day (F(7,126) = 52.41, p < 0.001), but no effect of Group (F(2,18) = 0.00, p = 1.00) and no Group × Day interaction (F(14,126) = 1.47, p = 0.131). These results indicate that all groups acquired the task about over the course of training, and any subsequent differences between groups during extinction may not be readily attributed to differing rates of initial task acquisition
Summary
Mammalian memory is not a unitary phenomenon, but rather it transpires through distinct systems. These ‘‘memory systems’’ differ in terms of the type(s) of memory they mediate, and the brain regions that subserve them. Extinction constitutes a new, dissociable type of learning that occurs when a subject is placed in the original learning situation but with the reinforcer—or the stimulus event that motivated initial learning—removed. Learned behavior in the straight alley maze, a maze in which rats learn to traverse a runway for food reward located at the opposite end of the maze, may be extinguished using two distinct protocols. During latent extinction, animals cannot execute the running approach response. The effectiveness of latent extinction figured prominently in learning theory, because it demonstrated that—in contrast to the Hullian S-R view of extinction (Hull, 1943, 1952)—a subject does not need to make the previously acquired response for extinction to occur (Seward and Levy, 1949; Deese, 1951; Moltz, 1955; Denny and Ratner, 1959; Dyal, 1962; Clifford, 1964)
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