Paradoxical sleep deprivation impairs acquisition, consolidation, and retrieval of a discriminative avoidance task in rats

The aim of the present study was to investigate the effects of paradoxical sleep deprivation (PSD) for 96 h on the learning/memory processes in rats submitted to the plus-maze discriminative avoidance task (PM-DAT), which simultaneously evaluates learning, memory, anxiety and motor function. Four experiments were performed in which rats were submitted to: (1) post-training and pre-test PSD; (2) post-training or pre-test PSD; (3) pre-training PSD or pre-training paradoxical sleep (PS) rebound (24 h) and (4) pre-test PSD rebound. Concerning Experiment I, post-training and pre-test PSD induced memory deficits, an anxiolytic-like behavior and an increase in locomotor activity. In Experiment II, both post-training PS-deprived and pre-test PS-deprived groups showed memory deficits per se. However, only the pre-test PS-deprived animals presented anxiolytic-like behavior and increased locomotor activity. In Experiment III, pre-training PS-deprived rats showed learning and memory deficits, anxiolytic-like behavior and increased locomotor activity. A 24h-sleep recovery period after the PSD abolished the learning and memory deficits but not anxiety and locomotor alterations. Finally, sleep rebound did not modify acquisition (Experiment III) and retrieval (Experiment IV). This study strengthened the critical role of paradoxical sleep (but not sleep rebound) in all the phases of learning and memory formation. In addition, it suggests that PSD effects on acquisition and consolidation do not seem to be related to other behavioral alterations induced by this procedure.     

Iterated Belief Revision, Reliability, and Inductive Amnesia

Belief revision theory concerns methods for reformulating an agent's epistemic state when the agent's beliefs are refuted by new information. The usual guiding principle in the design of such methods is to preserve as much of the agent's epistemic state as possible when the state is revised. Learning theoretic research focuses, instead, on a learning method's reliability or ability to converge to true, informative beliefs over a wide range of possible environments. This paper bridges the two perspectives by assessing the reliability of several proposed belief revision operators. Stringent conceptions of minimal change are shown to occasion a limitation called inductive amnesia: they can predict the future only if they cannot remember the past. Avoidance of inductive amnesia can therefore function as a plausible and hitherto unrecognized constraint on the design of belief revision operators.     

Stress and memory: opposing effects of glucocorticoids on memory consolidation and memory retrieval

It is well established that glucocorticoid hormones, secreted by the adrenal cortex after a stressful event, influence cognitive performance. Some studies have found glucocorticoid-induced memory enhancement. However, many studies have reported impairing effects of glucocorticoids on memory function. This paper reviews recent findings from this laboratory on the acute effects of glucocorticoids in rats on specific memory phases, i.e., memory consolidation and memory retrieval. The evidence suggests that the consequences of glucocorticoid activation on cognition depend largely on the different memory phases investigated. Posttraining activation of glucocorticoid-sensitive pathways involving glucocorticoid receptors enhances memory consolidation in a pattern highly similar to that previously described for adrenal catecholamines. Also, similar to catecholamine effects on memory consolidation, glucocorticoid influences on memory consolidation depend on noradrenergic activation of the basolateral complex of the amygdala and interactions with other brain regions. By contrast, memory retrieval processes are usually impaired with high circulating levels of glucocorticoids or following infusions of glucocorticoid receptor agonists into the hippocampus. The hypothesis is proposed that these apparently dual effects of glucocorticoids on memory consolidation and memory retrieval might be related and that the basolateral complex of the amygdala is a key structure in a memory-modulatory system that regulates, in concert with other brain regions, stress and glucocorticoid effects on both memory consolidation and memory retrieval.     

Amnesia,rehearsal, and temporal distinctiveness models of recall

Classical amnesia involves selective memory impairment for temporally distant items in free recall (impaired primacy) together with relative preservation of memory for recency items. This abnormal serial position curve is traditionally taken as evidence for a distinction between different memory processes, with amnesia being associated with selectively impaired long-term memory. However recent accounts of normal serial position curves have emphasized the importance of rehearsal processes in giving rise to primacy effects and have suggested that a single temporal distinctiveness mechanism can account for both primacy and recency effects when rehearsal is considered. Here we explore the pattern of strategic rehearsal in a patient with very severe amnesia. When the patient’s rehearsal pattern is taken into account, a temporal distinctiveness model can account for the serial position curve in both amnesic and control free recall. The results are taken as consistent with temporal distinctiveness models of free recall, and they motivate an emphasis on rehearsal patterns in understanding amnesic deficits in free recall.     

Encoding, consolidation, and retrieval of contextual memory: differential involvement of dorsal CA3 and CA1 hippocampal subregions

Studies on human and animals shed light on the unique hippocampus contributions to relational memory. However, the particular role of each hippocampal subregion in memory processing is still not clear. Hippocampal computational models and theories have emphasized a unique function in memory for each hippocampal subregion, with the CA3 area acting as an autoassociative memory network and the CA1 area as a critical output structure. In order to understand the respective roles of the CA3- and CA1-hippocampal areas in the formation of contextual memory, we studied the effects of the reversible inactivation by lidocaine of the CA3 or CA1 areas of the dorsal hippocampus on acquisition, consolidation, and retrieval of a contextual fear conditioning. Whereas infusions of lidocaine never impaired elementary tone conditioning, their effects on contextual conditioning provided interesting clues about the role of these two hippocampal regions. They demonstrated first that the CA3 area is necessary for the rapid elaboration of a unified representation of the context. Secondly, they suggested that the CA1 area is rather involved in the consolidation process of contextual memory. Third, they showed that CA1 or CA3 inactivation during retention test has no effect on contextual fear retrieval when a recognition memory procedure is used. In conclusion, our findings point as evidence that CA1 and CA3 subregions of the dorsal hippocampus play important and different roles in the acquisition and consolidation of contextual fear memory, whereas they are not required for context recognition.     

Amitriptyline administered after consolidation of inhibitory avoidance does not affect memory retrieval

In Experiment 1, the effect of the administration of the antidepressant amitriptyline (30 mg/kg) for 21 days on the acquisition and consolidation of the inhibitory avoidance task was studied in male and female mice. In Experiment 2, it was evaluated whether amitriptyline administered after the consolidation of this task would block the memory retrieval. Anxiety and spontaneous activity in the elevated plus maze were also assessed. When amitriptyline was given before the training phase of inhibitory avoidance it blocked learning in males and there was a tendency in the same direction in females. However, the drug administered between training and test phases did not affect conditioning. These effects of amitriptyline seem to be independent of its actions on anxiety and locomotor activity. It may be that the effects observed are related to the therapeutic effects of antidepressants.     

Differential role of the hippocampal endocannabinoid system in the memory consolidation and retrieval mechanisms

CB1 cannabinoid receptors are abundantly expressed in the brain, with large concentrations present in the hippocampus, a brain structure essential for memory processing. In the present study, we have investigated the possible modulatory role of the endocannabinoid system in the dorsal hippocampus upon the different phases of memory processing of an aversive task. AM251, a selective antagonist of CB1 receptors, and anandamide, an endogenous agonist of cannabinoid receptors, were bilaterally infused into the dorsal hippocampus of male Wistar rats either before training, immediately after training, or before test in the step-down inhibitory avoidance (IA) task. Results showed that pre-training infusion of CB1 drugs did not influence the acquisition of the task. In contrast, post-training infusion of the CB1 antagonist disrupted while the antagonist facilitated memory consolidation of IA. The post-training results demonstrate that memory consolidation depends on the integrity of the endocannabinoid system in the CA1 region of the dorsal hippocampus. While we still have no direct proof of endocannabinoids released there after an aversive task such as IA, these results suggests that (a) AM251 acts blocking the binding of endogenously released cannabinoids and (b) exogenously supplemented anandamide may be adding its contribution to the action of the endogenously released pool. Considering our data and the higher density of CB1 receptors present in the GABAergic interneurons, we propose them as the putative target of the endocannabinoid modulation of memory, a hypothesis that needs to be proven. In addition, pre-test infusion of the CB1 receptor antagonist facilitated while infusion of the agonist did not affect memory retrieval of IA. The completely opposite action of the same drug upon memory at the post-training (consolidation) and pre-test (recall) contexts suggests that some durable change took place in the CA1 region during the consolidation process that modified the logical attributes of the pharmacological response, i.e., the drug response changed from memory disruption to memory facilitation. A similar phenomenon was previously described by us in the M4 cholinergic muscarinic subsystem in the hippocampus for the same task (Diehl, F., Fürstenau, L. O., Sanchez, G., Camboim, C., de Oliveira Alvares, L., Lanziotti, V. B., et al. (2007). Facilitatory effect of the intra-hippocampal pretest administration of MT3 in the inhibitory avoidance task. Behavioral Brain Research, 177(2), 227-231), but the biological nature of such change in the local neural circuitry remains to be investigated.     

Amnesia and the generic image

It is pointed out that the fate of generic images has been studied little, if at all, in amnesias of organic origin. Observations are described in a case of alcoholic Korsakoff psychosis which appear to indicate that generic images are subject to Ribot's Law of Regression. The patient, a spinster of 57, with some talent for drawing, was asked to represent a number of objects, e.g. a woman dressed in the latest fashions, which might reasonably be regarded as, “generic” in nature. These drawings suggested that the patient's generic images were, in some cases at least, appropriate to an earlier period of her personal history. In general, this ante-dating effect was in good correspondence with the scope of the retrograde amnesia. Some implications of these findings for the psychological theory of memory are briefly discussed.     

Acute predator stress impairs the consolidation and retrieval of hippocampus-dependent memory in male and female rats

We have studied the effects of an acute predator stress experience on spatial learning and memory in adult male and female Sprague-Dawley rats. All rats were trained to learn the location of a hidden escape platform in the radial-arm water maze (RAWM), a hippocampus-dependent spatial memory task. In the control (non-stress) condition, female rats were superior to the males in the accuracy and consistency of their spatial memory performance tested over multiple days of training. In the stress condition, rats were exposed to the cat for 30 min immediately before or after learning, or before the 24-h memory test. Predator stress dramatically increased corticosterone levels in males and females, with females exhibiting greater baseline and stress-evoked responses than males. Despite these sex differences in the overall magnitudes of corticosterone levels, there were significant sex-independent correlations involving basal and stress-evoked corticosterone levels, and memory performance. Most importantly, predator stress impaired short-term memory, as well as processes involved in memory consolidation and retrieval, in male and female rats. Overall, we have found that an intense, ethologically relevant stressor produced a largely equivalent impairment of memory in male and female rats, and sex-independent corticosterone-memory correlations. These findings may provide insight into commonalities in how traumatic stress affects the brain and memory in men and women.     

Amnesia and second language learning

The ability of an anterograde amnesic C.S. to learn a second language is assessed. First, her claim that she learned Italian while amnesic was examined in a series of formal tests of Italian. Second, C.S. and her husband were tutored in French and her acquisition was compared to that of her husband's. Third, C.S.'s ability to learn other kinds of verbal material with practice was investigated. The implications of C.S.'s apparent ability to learn a second language in the presence of a severe deficit for memory for other kinds of verbal material is discussed.     

Amnesia,flashbacks, nightmares,and dissociation in aging concentration camp survivors

The current study examined to what extent war memories of Dutch survivors of Japanese/Indonesian concentration camps display characteristics that are often believed to be typical for traumatic memories. Twenty-nine survivors were interviewed about amnesia, flashbacks, nightmares and the sensory quality of their most upsetting war memories. In addition, they completed self-report scales measuring post-traumatic stress symptoms and dissociation. In contrast to prevailing notions, amnesia, flashbacks and nightmares were not typical for this sample. Neither were traumatic memories characterized by a particularly strong sensory loading. Post-traumatic stress symptoms were not related to dissociative experiences. At least for this group of aging survivors, it appears that the pathogenic potential of traumatic memories has more to do with their extremely aversive content than with a qualitatively different type of organization of these memories.     

Amnesia,folklore and folks: recovered memories in clinical practice

The concepts of loss of control and craving are reveiwed and relevant experimental findings are discussed. Speed of drinking is suggested as a behavioural measure of craving and an experiment is described to test the hypothesis that craving is primed by a moderate dose of alcohol (45 gms). The hypothesis was confirmed but only for the severely dependent alcoholics.     

Amnesia, traumatic brain injury, and posttraumatic stress disorder: a methodological inquiry

This study explored the relationship between mild traumatic brain injury (MTBI), amnesia, and posttraumatic stress disorder (PTSD). MTBI status and amnesia for the event were assessed in 307 consecutive admissions to a Level 1 Trauma Center. Amnesia did not always occur concurrently with MTBI: 18% of those with MTBI had full recall and over half had partial recall of the event. Just over 10% of participants developed PTSD by 12 months post-injury, with prevalence comparable across MTBI and non-MTBI groups. Non-significant differences in incidence of PTSD were apparent between those with full recall (9%), partial recall (14%) and no recall (7%). These data highlight the fact that PTSD may develop following trauma despite amnesia for the event, and illustrate the importance in both clinical and research settings of carefully examining the extent of amnesia.     

Associative asymmetry,availability, and retrieval

Associative frequency, the ease with which a word comes to mind in free association, is taken as a measure of general response availability. As expected from this view, in both controlled experiments and in reanalyses of previously published correlational data, high associative frequency words were judged to be more familiar and were easier to recall but harder to recognize than low associative frequency words, even with meaningfulness, imagery, length in letters, and frequency excluded as factors. When used as foils in a recognition experiment, high associative frequency words attracted more responses than low associative frequency words. In addition, associative frequency and meaningfulness correlated only moderately and had different patterns of correlations with other variables, suggesting that the number of associations leading to and from a word differ.     

Cognitive Procedural Learning in Amnesia

This group study examined the role of residual declarative memory and task-specific cognitive abilities for cognitive procedural learning in amnesia. 20 amnesic patients and 40 control subjects were studied, using four new cognitive tasks, as well as the Tower of Hanoi and a Mirror Reading task. On the cognitive tasks, but not on Mirror Reading, the learning of amnesic patients was significantly impaired relative to controls. Between- and within-group differences in learning were found to be statistically related to cognitive abilities that are involved in the processing of the procedural tasks. In amnesic patients, significant effects of residual declarative memory on learning scores were not observed, but there was indirect evidence for a role of memory in two tasks. The analysis of the correlative relationship between absolute procedural task performances and cognitive abilities indicated a prolonged dependence on nonspecific intellectual abilities in amnesic patients, suggesting a retarded transition to more advanced stages of skill acquisition.