A Longitudinal Study of Semantic Grouping Strategy Use in 6–11-Year-Old Children: Investigating Developmental Phases,the Role of Working Memory,and Strategy Transfer

This two-cohort longitudinal study on the development of the semantic grouping strategy had three goals. First, the authors examined if 6–7-year-olds are nonstrategic before becoming strategic after prompting at 8–9 years of age, and if 8–9-year-olds are prompted strategic before spontaneous strategy use at 10–11 years of age. Children 6–7 and 8–9 years old performed two sort-recall tasks (one without and one with a grouping prompt) at two time points separated 1.5 years from each other. Second, the authors investigated whether short-term or working memory capacity at time point 1 predicted recall in children who did or did not use the semantic grouping strategy 1.5 years later. Third, the authors investigated whether prompted strategic children and children who used the strategy spontaneously differed in strategy transfer to a new task. Developmental results confirmed previous cross-sectional results, but in a longitudinal two-cohort study 6–7-year-olds were nonstrategic, and became prompted strategic around 8–9 years of age, followed by spontaneous strategy use at age 10–11 years. The authors found that memory capacity was not predictive of later use of the strategy. New findings were that prompted strategic children were as equally able as spontaneously strategic children to transfer the strategy to a new task, albeit with smaller recall benefits.     

Stress and Adaptation

ABSTRACT— Animal models have contributed considerably to the current understanding of mechanisms underlying the role of stress in health and disease. Despite the progress made already, much more can be made by more carefully exploiting animals' and humans' shared biology, using ecologically relevant models. This allows a fundamental analysis of factors modulating individual adaptive capacity and hence individual vulnerability to disease. This article highlights an emerging scientific approach that uses a framework of interpretation that is more biologically oriented than previous approaches, to evaluate both the adaptive and maladaptive nature of the stress response in relation to existing environmental demands.     

Violent phenotype in SAL mice is inflexible and fixed in adulthood

Violence was shown to be qualitatively different from functional hyper‐aggression in mice selected for high aggression namely Short Attack Latency (SAL), Turku Aggressive (TA) and North Carolina (NC900) strains. This study aimed at investigating whether this adulthood violent phenotype as seen previously in the SAL mice is fixed and hence behaviorally inflexible right from day 1 of the experiment or consequential, i.e., subject to gradual change from functional aggression to violence. The functionally hyper‐aggressive strains namely TA and NC900 strains served as controls for the study. Methodologically, behavioral (in)flexibility was studied using the overall sequential structure of agonistic behavior. In particular, intra‐individual variations in the overall agonistic behavior as well as offensive, pre‐ and post‐offensive behavior transitions, directly related to the resident–intruder interactions were investigated. The SAL mice showed the least intra‐individual variation in their overall sequential agonistic structure as well as a fixed offense‐oriented agonistic behavior of highest magnitude when compared with the other strains. Additionally, the pre‐ and post‐ offensive transitions were most salient in the functionally hyper‐aggressive TA and NC900 strains, whereas virtually absent in the SAL mice. Thus, the violent behavior of the adult SAL mice is behaviorally inflexible or fixed, whereas the functionally hyper‐aggressive behavior of the adult TA and NC900 mice is behaviorally flexible and constantly adaptive to the opponent behavior, over 3 days of repeated resident–intruder interaction. Aggr. Behav. 35:430–436, 2009. © 2009 Wiley‐Liss, Inc.     

Dorsal and ventral striatal protein synthesis inhibition affect reinforcer valuation but not the consolidation of instrumental learning

The evidence for a role of the striatum in the acquisition of uncued instrumental responding is ambiguous. It has been shown that post-session infusions of anisomycin into the core of the nucleus accumbens (NAcc) impaired instrumental acquisition, but pre-training lesions of the NAcc suggest that it is not necessary. Recently, we demonstrated that the infusion of anisomycin into the anterior cingulate cortex impaired instrumental acquisition indirectly through a taste aversion. Thus, we hypothesized that post-session anisomycin infusions into the NAcc affected instrumental acquisition through an effect on reinforcer valuation. For the dorsal striatum, both post-session infusions of anisomycin and pre-training lesion studies suggest that neither the dorsolateral nor the dorsomedial striatum is necessary for the acquisition of instrumental responding. However, it has not been attempted to block plasticity in both regions concurrently, and we hypothesized that both regions independently contribute to acquisition through goal-directed and habitual learning. In the current experiments, we first replicated the effect of unprotected post-session anisomycin infusions into the NAcc on instrumental acquisition. Subsequently, we investigated the effect of protein synthesis inhibition in the NAcc and dorsomedial and dorsolateral striatum concurrently on instrumental acquisition, critically controlling for effects on reinforcer valuation. The anisomycin infusions induced an aversive state, but did not affect instrumental acquisition.     

Children's use of semantic organizational strategies is mediated by working memory capacity

In adults, the ability to apply semantic grouping strategies has been found to depend on working memory. To investigate this relation in children, two sort-recall tasks (one without and one with a grouping instruction) were administered to 6–12-year-olds. The role of working memory was examined by means of mediation analyses and by assessing whether children who successfully used the semantic grouping strategy had higher working memory capacity than did children who did not show such strategy use. Only children aged 8–12 were able to successfully use semantic grouping strategies (and 8–9-year-olds only after instruction), while strategy use was absent in 6–7-year-olds. Both types of analysis involving working memory suggested that, also in children, working memory (and not short-term memory) mediates the development of successful use of the semantic grouping strategy during both encoding and retrieval.     

Post-learning infusion of anisomycin into the anterior cingulate cortex impairs instrumental acquisition through an effect on reinforcer valuation

The integrity of the rodent anterior cingulate cortex (ACC) is essential for various aspects of instrumental behavior, but it is not clear if the ACC is important for the acquisition of a simple instrumental response. Here, it was demonstrated that post-session infusions of anisomycin into the rat ACC completely prevented the acquisition of instrumental responding. The experimental use of post-session intracranial infusions of plasticity inhibitors is assumed to affect local consolidation of plasticity, but not behavioral task performance. However, in associative appetitive conditioning, post-session intracranial infusion of pharmaco-active compounds could actually interfere with subsequent task performance indirectly through retrospective effects on the valuation of ingested rewards. Thus, it was subsequently demonstrated that the intracranial infusion of anisomycin into the ACC after sucrose pellet consumption significantly reduced subsequent pellet consumption, suggesting that the infusion of anisomycin into the ACC produced conditioned taste avoidance. In the third experiment, an innovative procedure was introduced that dissociated the effects of intracranial infusions after conditioning sessions on task-learning and unconditioned stimulus valuation. With this procedure, the infusion of anisomycin into the ACC after instrumental sessions did not affect instrumental reinforcer valuation or the acquisition of instrumental responding, suggesting that plasticity in the ACC is not necessary for the acquisition of instrumental behavior.The anterior cingulate cortex (ACC) in the rodent brain is the area of association cortex that is most intimately associated with movement control, as it has direct corticospinal projections to motor neurons (Miller 1987) and is intricately connected with motor and premotor cortex (Brecht et al. 2004; Wang et al. 2008), and movement-related discharges in motivated tasks have been observed in the ACC (Jung et al. 1998; Kargo et al. 2007). On the basis of these findings, the ACC has been described as the limbic motor cortex (Craig 2003). Indeed, it has been demonstrated that neural activity in the ACC codes for performed actions and observed appetitive outcomes (Lapish et al. 2008), suggesting that the ACC could be important for instrumental conditioning. However, it is currently unclear whether the role of the ACC in instrumental conditioning is restricted to relatively complex instrumental tasks with response conflict (Lapish et al. 2008) and high response efforts (Rudebeck et al. 2006), or whether it extends generally to the acquisition of a simple appetitively motivated instrumental response as well. For example, it has been reported that the acquisition of instrumental responding under variable ratio 2 schedule of reinforcement was impaired after presession intra-ACC infusions of the N-methyl-d-aspartate (NMDA) receptor antagonist AP-5 (McKee et al. 2007).However, the practical investigation of the neural basis of learning is complicated by what can be considered as “side effects” of manipulations that are intended to interfere selectively with learning mechanisms. Both pretraining lesions and presession infusions of pharmacological agents into specific brain regions can produce interference with basic task performance in addition to impairing task-related learning. This problem can be overcome by the use of infusions of pharmacological agents after a behavioral conditioning session, specifically to target the consolidation of learning. Positive effects of post-session intracranial infusions of protein synthesis inhibitors such as anisomycin (Rosenblum et al. 1993), or NMDA, and dopamine receptor antagonists such as AP-5 or SCH 23390 (Dalley et al. 2005) on the acquisition of conditioned responses can be interpreted more confidently in terms of interference with learning, at least when combined with negative effects in delayed-infusion control groups. Certainly, positive effects of post-session infusions on learning in the absence of effects of delayed control infusions cannot be attributed to interference with task performance.Nevertheless, post-session intracranial infusions may still cause confounding effects on conditioned behavior in appetitive conditioning experiments, by changing the valuation of the unconditioned stimulus (US), or reward, in subsequent sessions. Such manipulations could reduce the valuation of rewards either through interference with consolidation or reconsolidation of the sensory or motivational properties of the US (Wang et al. 2005; Pedroza-Llinás et al. 2009), which would lead to persistent neophobia, or through retrospective devaluation of the task reward through the post-ingestion induction of an aversive state. Neither effect would be expected to be apparent in delayed-infusion control conditions. Furthermore, considering that animals typically earn far fewer rewards in conditioning sessions than they would maximally consume if rewards were freely available, such effects would not necessarily be visible in terms of consumption of earned rewards and unaffected latencies to collect rewards.In view of these considerations, the effect of the infusion of anisomycin into the rat ACC after instrumental sessions on the acquisition of conditioned responding was investigated. Based on the obtained results, it was further investigated whether the infusion of anisomycin into the ACC after free consumption of a novel reward would affect subsequent pellet consumption. Finally, a third experiment was conducted that introduced an innovative procedure that was designed to dissociate the effects of intracranial infusion of protein synthesis inhibitors after conditioning sessions on task-learning and US valuation.