Neural circuits mediating latent learning and conditioning for salt in the rat

Male Long-Evans rats alternately drank a salt solution in one distinctive compartment of a conditioned cue preference (CCP) apparatus and water in a different compartment over 8 days (training trials) and were then given a choice between the two compartments with no solutions present (test trial). Rats that were water deprived during training, then salt+water deprived during testing, spent more time in their salt-paired compartments, a salt latent cue preference (LCP). Rats that were water-only deprived during training and testing spent more time in their water-paired compartments, a water CCP. Rats that were salt+water deprived during both training and testing spent more time in their salt-paired compartments, a salt CCP. Bilateral, pre-training lesions of the lateral amygdala impaired the water and salt CCPs but not the salt LCP, reflecting the role of the amygdala in Pavlovian conditioning. Lesions of the dorsal or ventral hippocampus impaired the salt LCP and the water and salt CCPs, possibly reflecting the role of the hippocampus in contextual learning. Lesions of the fimbria-fornix impaired the water and salt CCPs but not the salt LCP, while lesions of the entorhinal cortex impaired the salt LCP but not the CCPs. This suggests that the LCP depends on a circuit that includes dorsal and ventral hippocampus and entorhinal cortex, a major conduit of sensory information from the cortex. In contrast, the CCPs depend on the amygdala and a circuit that includes the hippocampus and fimbria-fornix, possibly as a conduit of motivational information from subcortical structures.     

Looking on the bright side: downward counterfactual thinking in response to negative life events

Past research has found that downward counterfactual thoughts are rarely generated in response to negative life events. However, the authors suggest that under conditions in which self-enhancement motives are prominent, downward counterfactuals will be more frequent than upward counterfactuals. When motives were explicitly manipulated (Study 1), people generated more downward counterfactuals in the self-enhancement than in the self-improvement and control conditions. In Study 2, among those chronically more motivated to self-enhance (i.e., European Canadians), a manipulation of event severity led to the generation of more downward than upward counterfactuals. This finding was mediated by the desire for self-enhancement. In Study 3, cultural background and the opportunity for self-affirmation were related to the generation of downward counterfactuals in expected ways. Implications of these findings are discussed.     

Integration of multiple speech segmentation cues: a hierarchical framework

A central question in psycholinguistic research is how listeners isolate words from connected speech despite the paucity of clear word-boundary cues in the signal. A large body of empirical evidence indicates that word segmentation is promoted by both lexical (knowledge-derived) and sublexical (signal-derived) cues. However, an account of how these cues operate in combination or in conflict is lacking. The present study fills this gap by assessing speech segmentation when cues are systematically pitted against each other. The results demonstrate that listeners do not assign the same power to all segmentation cues; rather, cues are hierarchically integrated, with descending weights allocated to lexical, segmental, and prosodic cues. Lower level cues drive segmentation when the interpretive conditions are altered by a lack of contextual and lexical information or by white noise. Taken together, the results call for an integrated, hierarchical, and signal-contingent approach to speech segmentation.     

Local proactive interference in delayed matching to sample: the role of reinforcement

Discriminability in delayed matching to sample was lower when the samples on consecutive trials differed compared with when samples on consecutive trials were the same. This local proactive interference occurred when correct choices on the previous trial were reinforced but not when correct choices on the previous trial were not reinforced. When the choice on the previous trial was incorrect, discriminability was higher on different consecutive trials than on same trials. These effects were amplified by varying the ratio of reinforcers for correct choices, as predicted by a model that attributes local proactive interference to an interaction between control by the sample on the current trial and the influence of reinforcers for correct choices on previous trials.     

The role of stimulus ambiguity and movement in spatial navigation: a multiple memory systems analysis of location discrimination

This paper reviews recent findings about how rats navigate by learning to discriminate among locations. The assumption underlying the experiments and their interpretation is that the information required to do this is learned by three independent, parallel memory systems. One system processes cognitive information (or "knowledge"), a second system processes reinforced stimulus-response associations and a third processes Pavlovian conditioned responses in the form of stimulus-affect associations. The information stored in each system produces behavior that, in some cases, results in a location discrimination. The present experiments focus on three factors that influence what each system learns and whether the resulting memory produces behavior that results in a location discrimination. One factor is whether the locations to be discriminated can be identified by unique, unambiguous stimuli or whether they are ambiguously associated with the same stimuli. The second factor is whether the stimuli are observed passively or whether the rats move among them, voluntarily or involuntarily. The third factor is whether or not the rats perform specific reinforced responses in the presence of the stimuli. Instances of co-operative behavioral outputs from memory systems that facilitate location discriminations and of competitive outputs that impede discriminations are described.     

Instructions for Authors

Instructions for Authors

Instructions for Authors     

Instructions for Authors

Instructions for Authors

Instructions for Authors     

A case-control analysis of felony convictions among recreational drug users

This study applied an epidemiologic case-control design to the identification of variables predicting which subjects in a population of recreational drug users were likely to have a felony conviction. A sample of 158 self-identified drug users responded to the web-based DRUGNET survey from February, 1997 through June, 1998. In this sample of 704 U.S. citizens who reported using illicit drugs, 79 (11.2%) reported having a drug-related felony conviction. A further 52 (7.4%) subjects reported felony convictions not related to drugs. Control subjects were drawn from the same sample and matched to cases on sex, age, and ethnicity. Subjects with drug-related convictions differed significantly from controls on 13 variables and those with nondrug-related convictions differed on 11 variables out of the 82 used in this study. Although there are major limitations given the self-selection of the sample, the differences between the groups indicates that we should be wary in generalizing from the minority of drug users who are arrested or incarcerated to the population of drug users in general.