Systemic and local administration of estradiol into the prefrontal cortex or hippocampus differentially alters working memory

The influence of estradiol on learning and memory is dependent on a number of factors. The effects of physiological levels of estradiol on the acquisition of a spatial working memory task mediated by the prefrontal cortex (PFC) and the hippocampus were examined in Experiment 1. Ovariectomized Long-Evans rats received daily injections of estradiol or vehicle were tested on the win-shift version of the radial arm maze. A high dose of estradiol benzoate (5 microg) enhanced acquisition of the task, whereas a low dose of estradiol (0.3 microg) increased the number of errors committed over 17 days of testing. Experiment 2 was conducted to examine site-specific influences of estradiol on spatial working memory in well-trained rats. Saline and estradiol cyclodextrin (0.1 and 0.9 microg) were infused into the prelimbic region of the PFC or dorsal hippocampus 40 min prior to testing on the win-shift task. Infusions of estradiol into both brain areas attenuated saline-infusion disruptions in working memory. Specifically, the higher dose of estradiol facilitated working memory when infused into the PFC, whereas the lower dose of estradiol facilitated performance when infused into the dorsal hippocampus. Moreover, working memory was significantly impaired 24 h after infusions of estradiol into the dorsal hippocampus but not the PFC. These data provide further evidence for the notion that estradiol can dose-dependently alter memory processes and suggest that facilitation or disruptions of working memory by estradiol are site- and time-specific.     

Inhibition and shifting in children with learning deficits in arithmetic and reading

The executive functions of inhibition and shifting were studied in arithmetic-disabled children, reading-disabled children, reading plus arithmetic-disabled children, and controls (N = 74). Measures involved the rapid naming of objects, digits, letters, or quantities with or without additional task requirements that reflected inhibition or shifting. Also, the Making Trails task, reflecting shifting, was administered. For tasks without executive demands, arithmetic-disabled children were slower in the naming of digits and quantities, whereas reading-disabled children were slower in the naming of digits and letters. For the executive tasks, arithmetic-disabled children as well as reading plus arithmetic-disabled children were impaired on the Making Trails task and on an object naming task that required both inhibition and shifting. Reading-disabled children exhibited no problems in executive functioning. Furthermore, it was shown that reading plus arithmetic-disabled children experienced the combination of problems that characterize children with a single learning deficit.     

Learning and transfer from a simple dynamic system

The amount of learning gained from being assisted in completing the task of bringing a predator-prey system into equilibrium by controlling the predator population was investigated. Learning was explored both by post-task questioning and by testing for transfer to another predator-prey task. Participants were 28 undergraduate psychology students, all female. They were randomly and evenly split into an experiment group that was subjected to a learning session with the first task before being tested in the second task, and a control group that only performed the second task. What was most needed in the first task was help in sticking to analytically derived conclusions by resisting "common sense" responses. There was a significant transfer effect on performance to the second task, stemming from learning shown by half the participants in the experiment group. The other half showed hardly any learning. Learning in about half the subjects has proven a stable finding.     

Modeling parallelization and flexibility improvements in skill acquisition: from dual tasks to complex dynamic skills

Emerging parallel processing and increased flexibility during the acquisition of cognitive skills form a combination that is hard to reconcile with rule-based models that often produce brittle behavior. Rule-based models can exhibit these properties by adhering to 2 principles: that the model gradually learns task-specific rules from instructions and experience, and that bottom-up processing is used whenever possible. In a model of learning perfect time-sharing in dual tasks (Schumacher et al., 2001), speedup learning and bottom-up activation of instructions can explain parallel behavior. In a model of a complex dynamic task (Carnegie Mellon University Aegis Simulation Program [CMU-ASP], Anderson et al., 2004), parallel behavior is explained by the transition from serially organized instructions to rules that are activated by both top-down (goal-driven) and bottom-up (perceptually driven) factors. Parallelism lets the model opportunistically reorder instructions, leading to the gradual emergence of new task strategies.     

Hippocampal c-fos is necessary for long-term memory of a socially transmitted food preference

The present article examined the requirement of hippocampal c-Fos for learning a socially transmitted food preference (STFP). We reported previously that expression of the c-Fos protein is increased in the dorsal and ventral hippocampus of rats trained on the STFP (Countryman, Orlowski, Brightwell, Oskowitz, & Colombo, 2005). Pretraining intrahippocampal antisense to the immediate early gene c-fos was administered to adult male Long-Evans rats to determine if c-fos expression is necessary for either short- or long-term memory for STFP. Guide cannulae were implanted bilaterally into the dorsal hippocampus. Antisense oligodeoxynucleotides (ODNs) were administered unilaterally either 6.5, 8.5, 10.5, or 12.5 h prior to STFP training while either sense ODNs or saline were infused into the opposite hemisphere. Immunocytochemistry was performed, and cells showing c-Fos immunoreactivity (ir) were counted from the antisense-treated hemisphere and compared to cell counts from the control hemisphere. The results indicated significant suppression of learning-induced c-Fos protein at the 8.5 and 10.5 infusion-train intervals. Additional rats were implanted with cannulae into the dorsal and ventral hippocampus, and antisense ODNs, sense ODNs, or saline were administered bilaterally 8.5h prior to training. Rats were tested immediately and 14 days after training. Rats in all groups showed a significant preference for the demonstrated food at the short-term memory test. At the long-term memory test, however, rats infused with c-fos antisense showed no preference for the demonstrated food whereas rats infused with either sense or saline maintained their preference. The present findings suggest that c-fos is necessary for consolidation of non-spatial hippocampal-dependent memory.     

Acquiring new spatial intuitions: learning to reason about rotations

There are certain simple rotations of objects that most people cannot reason about accurately. Reliable gaps in the understanding of a fundamental physical domain raise the question of how learning to reason in that domain might proceed. Using virtual reality techniques, this project investigated the nature of learning to reason across the domain of simple rotations. Learning consisted of the acquisition of spatial intuitions: there was encoding of useful spatiotemporal information in specific problem types and a gradual accumulation of this understanding across the domain. This pattern of learning through the accumulation of intuitions is especially interesting for rotational motion, in which an elegant domain-wide kinematics is available to support insightful learning. Individual ability to reason about rotations correlated highly with mastery motivation, skill in fluid reasoning, and skill in reasoning about spatial transformations. Thus, general cognitive advantages aided the understanding of individual rotations without guaranteeing immediate generalization across the domain.     

Speech segmentation by statistical learning depends on attention

We addressed the hypothesis that word segmentation based on statistical regularities occurs without the need of attention. Participants were presented with a stream of artificial speech in which the only cue to extract the words was the presence of statistical regularities between syllables. Half of the participants were asked to passively listen to the speech stream, while the other half were asked to perform a concurrent task. In Experiment 1, the concurrent task was performed on a separate auditory stream (noises), in Experiment 2 it was performed on a visual stream (pictures), and in Experiment 3 it was performed on pitch changes in the speech stream itself. Invariably, passive listening to the speech stream led to successful word extraction (as measured by a recognition test presented after the exposure phase), whereas diverted attention led to a dramatic impairment in word segmentation performance. These findings demonstrate that when attentional resources are depleted, word segmentation based on statistical regularities is seriously compromised.     

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.     

Acetylcholine actions in the dorsomedial striatum support the flexible shifting of response patterns

There is accumulating evidence that the dorsomedial striatum plays a significant role in the learning of a new response pattern and the inhibiting of old response patterns when conditions demand a shift in strategies. This paper proposes that activity of cholinergic neurons in the dorsomedial striatum is critical for enabling behavioral flexibility when there is a change in task contingencies. Recent experimental findings are provided supporting this idea. Measuring acetylcholine efflux from the dorsomedial striatum during the acquisition and reversal learning of a spatial discrimination shows that acetylcholine efflux selectively increases during reversal learning as a rat begins to learn a newly reinforced spatial location, but returns to near basal levels when a rat reliably executes the new choice pattern. Experimental findings are also described indicating that the blockade of muscarinic cholinergic receptors in the dorsomedial striatum does not impair acquisition of an egocentric response discrimination, but impairs reversal learning of an egocentric response discrimination. Based on these results, increased cholinergic activity at muscarinic receptors is part of a neurochemical process in the dorsomedial striatum that allows inhibition of a previously relevant response pattern while learning a new response pattern. In situations that demand behavioral flexibility, muscarinic cholinergic activity in the dorsomedial striatum may directly influence corticostriatal plasticity to produce changes in response patterns.     

The developmental course of processing speed in children with and without learning disabilities

This study contrasted the development of processing speed in children with and without learning disabilities. We examined whether the same global mechanism presumed to be responsible for the normal developmental improvement in processing speed might also be associated with the processing speed deficiencies observed in children with learning impairments. One hundred and twenty-two children with learning disabilities in reading and/or math and 206 non-disabled community controls participated. There were no differences in relation of age to the development of processing speed for children with and without learning disabilities. We interpreted these results as suggesting that the underlying etiologies for the normal developmental change in processing speed and for the relative deficiencies in processing speed seen among children with learning disabilities were different.