Place learning in scopolamine-treated rats: the roles of distal cues and catecholaminergic mediation

Experiments 1 and 2 tested the hypothesis that cholinergic receptor antagonists impair place learning in a water maze by interfering with the processing of distal, visual cues. Extramaze cues were offered to rats in the form of geometrical patterns arranged on the inner circumference of a curtain surrounding the water maze. In Experiment 1 the animals were offered both the distal cues and proximal cues in the form of pingpong balls in fixed positions on the surface of the water while only distal cues were present in Experiment 2. Animals were injected with either scopolamine (0.5 mg/kg body wt) or saline 20 min prior to the daily place learning sessions. Upon reaching criterion level performance the animals were tested on "rotation" sessions on which the distal cues were displaced. The outcome of such "rotations" demonstrated that-regardless of the presence or absence of proximal cues-scopolamine-treated rats relied at least as much as normal animals on the distal cues. The acquisition phase of both Experiments 1 and 2 demonstrated an almost complete lack of scopolamine-associated impairment in acquisition and performance of the place learning task. In Experiment 3 (when scopolamine was no longer administered) the subjects of Experiment 2 were exposed to a series of pharmacological "challenges" of their place learning performance and eventually to surgical ablation of the anteromedial prefrontal cortex. The outcome of the pharmacological challenges and the postoperative test of task performance demonstrated that the place learning performance of animals which had acquired the task under scopolamine was mediated by a neural substrate dissimilar to the substrate of task performance in normal animals. Rats acquiring the task while deprived of the cholinergic system demonstrated above-normal contributions to task mediation from catecholaminergic-probably dopaminergic-mechanisms and tentative results pointed to a "shift" toward prefrontal task mediation.     

Retrieval improvement is induced by water shortage through angiotensin II

Angiotensin II (ANGII) has an evolutionary preserved role in determining adaptative responses to water-shortages. In addition, it has been shown to modulate diverse phases of memory. Still, it is not clear whether ANGII improves or spoils memory. We demonstrated that endogenous angiotensins enhance consolidation of a long-term associative memory in the crab Chasmagnathus and that water shortage improves memory consolidation through brain ANGII actions. Here, we show that weakly trained crabs, when water-deprived, exhibit enhanced retrieval. Subsequently, memory retention is indistinguishable from that of strongly trained crabs. ANGII, but not angiotensin IV, is a necessary and sufficient condition for such enhancing effect. We conclude that ANGII released due to water shortage leads to enhanced memory retrieval. Thus, it seems that ANGII has an evolutionary preserved role as a multifunction coordinator that enables an adaptative response to water-shortage. The facilitation of memory consolidation and retrieval would be among those coordinated functions.     

Relationship between short- and long-term memory and short- and long-term extinction

Both the acquisition and the extinction of memories leave short- and long-term mnemonic traces. Here, we show that in male Wistar rats, the short-term memory for a step-down inhibitory avoidance task (IA) is resistant to extinction, and that its expression does not influence retrieval or extinction of long-term memory. It has been known for some time that short- and long-term inhibitory avoidance memory involve separate and parallel processes. Here we show that, instead, short-term extinction of IA long-term memory is the first step towards its long-term extinction, and that this link requires functional NMDA receptors and protein synthesis in the CA1 region of the dorsal hippocampus at the time of the first CS-no US presentation.     

Learning new names for new objects: cortical effects as measured by magnetoencephalography

We tracked the evolvement of naming-related cortical dynamics with magnetoencephalography when five normal adults successfully learned names and/or meanings of unfamiliar objects. In all subjects, the learning of new names was associated with pronounced cortical effects. The learning effect was of long latency and emerged as a change of activation in the same cortical network that was active during naming of familiar items. In four out of five subjects, the cortical learning effect occurred in the inferior parietal lobe. In three of these subjects, the cortical effect was left-sided. These results suggest that the inferior parietal lobe plays an important role in the acquisition of novel words, presumably as a part of working memory systems.     

What do computer models of cognition explain: a reply to Gobet

The differences between Gobet’s views and ours call attention to some points concerning the argumentative status of computational models. If we have two fundamentally different models which reasonably accurately simulate a phenomenon, we must ask, what is the argumentative status of the models in psychological terms. Moreover, if it is possible to present different models of same phenomena, what is the general argumentative power of models in psychology? As the kind of differences between our views and the ones of Gobet’s are common in modelling, we briefly call attention to these foundational issues in our paper.     

Comparative evaluations of reward dimensions in honey bees: evidence from two-alternative forced choice proboscis-extension conditioning

A major challenge in understanding choice behaviour is determining how subjects evaluate alternatives that differ along multiple dimensions. Of particular interest is whether similar dimensions are compared to each other or whether each alternative is assigned an absolute value (utility). We assumed that choice proportions would follow Weber’s effect, according to which discrimination is proportional to relative difference (difference/mean). We tested honey bees in a two-alternative forced choice (2AFC) paradigm of proboscis-extension response (PER) conditioning. Subjects were conditioned over six trials to associate each of two odours with sucrose solution rewards and then tested in a choice trial between the two alternatives. Each group of subjects was tested in one treatment, and there were four treatments in each of six experiments. Rewards differed in delay, duration of feeding, and sucrose concentration. In each treatment, the high-profitability alternative was better than the low-profitability alternative along a single dimension, but between treatments of each experiment values in another dimension monotonically increased. Proboscis-response proportions during the conditioning phase tended to be greater for the high-profitability alternative, and choice proportions for it in the choice phase ranged between 0.72 and 0.89 in the 24 treatments. We show for the first time that harnessed bees are sensitive to reward delay. Preferences did not differ statistically between the different treatments of any of the experiments. The results support comparative evaluation of alternatives and are pertinent to multi-attribute choice, with implications for context-dependent preferences. We also discuss the potential advantages of the 2AFC PER simultaneous choice assay.     

More Than Words: Fast Acquisition and Generalization of Orthographic Regularities During Novel Word Learning in Adults

In literates, reading is a fundamental channel for acquiring new vocabulary both in the mother tongue and in foreign languages. By using an artificial language learning task, we examined the acquisition of novel written words and their embedded regularities (an orthographic surface feature and a syllabic feature) in three groups of university students with different exposures (Group 1 saw 2 words once, Group 2 saw 20 words once, Group 3 saw 20 words three times). Recognition memory results for Groups 2 and 3 indicated that adults can learn novel written words even with just a single exposure, albeit repeated exposure improved target detection. A generalization task revealed that even the minimal exposure in Group 1 was enough for acquisition of the two embedded regularities. More exemplars and repeated exposure provided more robust effects for the syllable regularity. Finally, post-test interview showed that repeated exposure was needed to become aware of the regularities. The present results show that adults learn novel written words and their inherent regularities in a fast and effective fashion.     

Histamine enhances inhibitory avoidance memory consolidation through a H2 receptor-dependent mechanism

Several evidences suggest that brain histamine is involved in memory consolidation but the actual contribution of the hippocampal histaminergic system to this process remains controversial. Here, we show that when infused into the CA1 region of the dorsal hippocampus immediately after training in an inhibitory avoidance task, but not later, histamine induced a dose-dependent promnesic effect without altering locomotor activity, exploratory behavior, anxiety state or retrieval of the avoidance response. The facilitatory effect of intra-CA1 histamine was mimicked by the histamine N-methyltransferase inhibitor SKF-91844 as well as by the H2 receptor agonist dimaprit and it was blocked completely by the H2 receptor antagonist ranitidine. Conversely, the promnesic action of histamine was unaffected by the H1 receptor antagonist pyrilamine, the H3 receptor antagonist, thioperamide, and the NMDAr polyamine-binding site antagonist ifenprodil. By themselves, ranitidine, pyrilamine, thioperamide, and ifenprodil did not affect IA memory consolidation. Our data indicate that, when given into CA1, histamine enhances memory consolidation through a mechanism that involves activation of H2 receptors; however, endogenous CA1 histamine does not seem to participate in the consolidation of IA memory at least at the post-training times analyzed.     

Neural correlates of morphological decomposition in a morphologically rich language: an fMRI study

By employing visual lexical decision and functional MRI, we studied the neural correlates of morphological decomposition in a highly inflected language (Finnish) where most inflected noun forms elicit a consistent processing cost during word recognition. This behavioral effect could reflect suffix stripping at the visual word form level and/or subsequent meaning integration at the semantic-syntactic level. The first alternative predicts increased activation for inflected vs. monomorphemic words in the left occipitotemporal cortex while the second alternative predicts left inferior frontal gyrus and/or left posterior temporal activation increases. The results show significant activation effects in the latter areas. This provides support for the second alternative, i.e., that the morphological processing cost stems from the semantic-syntactic level.