Learning in a unidimensional absolute identification task

We tested whether there is long-term learning in the absolute identification of line lengths. Line lengths are unidimensional stimuli, and there is a common belief that learning of these stimuli quickly reaches a low-level asymptote of about seven items and progresses no more. We show that this is not the case. Our participants served in a 1.5-h session each day for over a week. Although they did not achieve perfect performance, they continued to improve day by day throughout the week and eventually learned to distinguish between 12 and 20 line lengths. These results are in contrast to common characterizations of learning in absolute identification tasks with unidimensional stimuli. We suggest that this learning reflects improvement in short-term processing.     

Spatial and non-spatial visual discrimination learning in zebrafish (Danio rerio)

Zebrafish (Danio rerio) provide an excellent model for assessment of molecular processes of neurodevelopment. To determine the functional importance of molecular events during neurodevelopment, we have developed methods for assessing learning in zebrafish in a three-chambered fish tank. In the first study, simple escape response was assessed. Zebrafish tested with a moving net learned to escape to another chamber more rapidly over the six sessions of training than the fish with the still net which did not learn. Upon reversal of the contingencies, the fish switched to the inactive net rapidly learned to suppress the escape response and fish formerly in the inactive net condition learned to avoid the moving net. In the second study, spatial discrimination learning was assessed. Zebrafish were trained on a right-left position discrimination to avoid the active net. Zebrafish showed significant improvement in escape responses over six sessions of training with three trials per session. In the third study, red-blue non-spatial discrimination learning was assessed. There was a significant improvement over the first six training sessions. With the reversal of contingencies, there was a significant decline of performance. With continued training, the fish again significantly improved avoidance. These studies found an effective motivational stimulus and procedure for studying escape behavior in zebrafish; a procedure whereby zebrafish would learn both spatial and non-spatial discrimination. These methods are being developed to help determine the functional importance of molecular events during zebrafish neurodevelopment. Accepted after revision: 20 August 2001 Electronic Publication     

Spatial cognition in zebrafish: the role of strain and rearing environment

Two strains of zebrafish, WIK and a second-generation wild strain were reared in either a structurally simple or complex environment and compared in their ability to locate a food reward in a five-chambered maze. There was a significant interaction within subjects between rearing environment and trial, indicating that the consistency of learning varied depending on rearing environment, with those reared in a structurally simple environment showing a slower rate of learning. Fish of both strains reared in a structurally complex environment were smaller than those reared in a simple environment. Our study demonstrates, for the first time in zebrafish, that performance in a learning task as an adult is sensitive to rearing conditions during development.     

A one-trial inhibitory avoidance task to zebrafish: Rapid acquisition of an NMDA-dependent long-term memory

The behavioral tasks aiming to evaluate learning and memory mechanisms currently available to zebrafish (Danio rerio) involve long training sessions frequently along multiple days and are based on shuttle box or active-avoidance protocols, preventing a detailed analysis of cellular and molecular time-dependent processes involved in memory acquisition and consolidation. In order to explore zebrafish’s potential contribution to the characterization of the molecular machinery underlying learning and memory rapidly acquired and reliable paradigms are necessary. In this study we present a rapid and effective learning protocol in a single-trial inhibitory avoidance in zebrafish. In a simple apparatus, adult animals learned to refrain from swimming from a white into a dark compartment in order to avoid an electric shock during a single-trial training session that lasted less than 2 min. The resulting memory is robust, long-lasting and sensitive to NMDA-receptor antagonist MK-801 given in the tank water immediately after training. Experiments aiming to further characterize the events underlying memory formation, retrieval or extinction or those looking for cognitive profiling of mutants, neurotoxicological studies and disease models may benefit from this task, and together with complementary strategies available for zebrafish may significantly improve our current knowledge on learning and memory mechanisms.     

Differences in the complexity of song tutoring cause differences in the amount learned and in dendritic spine density in a songbird telencephalic song control nucleus

In our search for relations between vocal learning and neuron structure in the song control nuclei of songbird forebrains, we tested whether differential experience that leads to differences in adult song repertoire would affect dendritic spine density in HVc (also called high vocal center) and RA (robustus archistriatalis). We tape-tutored juvenile Eastern marsh wrens (Cistothorus palustris) with either 5 or 45 song types. As adults, the small repertoire group had learned mostly 5 or 6 song types, and the large repertoire group had learned 36 to 47. Wrens that learned the large song repertoires had a greater dendritic spine density for the most spiny neurons present in HVc (mean difference, 36%), but not in RA. Recent physiological evidence describes HVc as a premotor area coding syllables, motifs, and higher-order song patterns, and our data now clearly reveal that differences in the size of the song repertoire that is experienced lead to differences both in song learning and in the density of dendritic spines in HVc. In the forebrain song nuclei of these songbirds, as in some other vertebrate systems, differences in learning and performance are associated with differences in synaptic anatomy specifically in the region that organizes the learned pattern.     

Active avoidance conditioning in zebrafish (Danio rerio)

The zebrafish represents a potentially useful organism for studying genes involved in learning and memory function in vertebrates, because a number of genetic techniques in zebrafish have been developed to produce a wide variety of genetic mutants. While zebrafish mutants are being developed, behavioral studies on learning and memory function in zebrafish are in urgent need. The present study investigated active avoidance conditioning in normal zebrafish. Zebrafish were trained to swim from a lighted (CS) compartment to a dark compartment to avoid an electrical body shock (US) in a shuttle-box that consisted of a water-filled tank separated by an opaque barrier into two equal compartments. By varying the number of trials per training session and the duration of the intertrial interval, Experiments 1 and 2 showed that, with the CS, US, and intertrial interval being 12s, zebrafish learned avoidance responses within a training session consisting of 30 trials and retained the avoidance responses. Experiment 3 showed that zebrafish learned avoidance responses following the association between the CS of light and the US of shock in the avoidance conditioning paradigm. Using the avoidance conditioning paradigm, Experiment 4 investigated the amnestic effects of N-methyl-D-aspartate receptor antagonist MK-801 and nitric oxide synthase inhibitor L-NAME in zebrafish. Experiment 4 showed that post-training injection of L-NAME significantly impaired retention of avoidance responses while MK-801 did not, confirming previous results with other vertebrates. The results of the present study suggest the similar involvements of neurochemicals in learning and memory among vertebrates. Thus, future studies with zebrafish mutants may identify genes involved in learning and memory in vertebrates.     

Neurogenesis and learning: acquisition and asymptotic performance predict how many new cells survive in the hippocampus

Previous research has shown that some associative learning tasks prevent the death of new neurons in the adult hippocampus. However, it is unclear whether it is mere exposure to the training stimuli that rescues neurons or whether successful learning of the task is required for enhanced neuronal survival. If learning is the important variable, then animals that learn better given the same amount of training should retain more of the new cells after learning than animals that do not learn as well. Here, we examined the effects of training versus learning on cell survival in the adult hippocampus. Animals were injected with BrdU to label a population of cells and trained one week later on one of two trace conditioning tasks, one of which depends on the hippocampus and one that does not. Increases in cell number occurred only in animals that acquired the learned response, irrespective of the task. There were significant correlations between acquisition and cell number, as well as between asymptotic performance and cell number. These data support the idea that learning and not simply training increases the survival of the new cells in the hippocampus.     

Coordination dynamics of learning and transfer across different effector systems

If different effector systems share a common task-specific coordination dynamics, transfer and generalization of sensorimotor learning are predicted. Subjects learned a visually specified phase relationship with either the arms or the legs. Coordination tendencies in both effector systems were evaluated before and after practice to detect attractive states of the coordination dynamics. Results indicated that learning a novel relative phase with a single effector system spontaneously transferred to the other, untrained effector system. Transfer was revealed not only as improvements in performance but also as modifications of each system's initial (prelearning) coordinative landscape. What is learned, appears to be a high-level but neurally instantiated dynamic representation of skilled behavior that proves to be largely effector independent, at least across anatomically symmetric limbs.     

Hippocampal theta (3-8Hz) activity during classical eyeblink conditioning in rabbits

In 1978, Berry and Thompson showed that the amount of theta (3–8 Hz) activity in the spontaneous hippocampal EEG predicted learning rate in subsequent eyeblink conditioning in rabbits. More recently, the absence of theta activity during the training trial has been shown to have a detrimental effect on learning rate. Here, we aimed to further explore the relationship between theta activity and classical eyeblink conditioning by determining how the relative power of hippocampal theta activity [theta/(theta + delta) ratio] changes during both unpaired control and paired training phases. We found that animals with a higher hippocampal theta ratio immediately before conditioning learned faster and also that in these animals the theta ratio was higher throughout both experimental phases. In fact, while the hippocampal theta ratio remained stable in the fast learners as a function of training, it decreased in the slow learners already during unpaired training. In addition, the presence of hippocampal theta activity enhanced the hippocampal model of the conditioned response (CR) and seemed to be beneficial for CR performance in terms of peak latency during conditioning, but did not have any effect when the animals showed asymptotic learning. Together with earlier findings, these results imply that the behavioral state in which hippocampal theta activity is absent is detrimental for learning, and that the behavioral state in which hippocampal theta activity dominates is beneficial for learning, at least before a well-learned state is achieved.     

Non-specific effect of fear conditioning and specific effect of social defeat on social recognition memory performance in female rats

The so called "emotion learning" literature describes the ability of distressing and aversive unconditioned stimuli to classically condition a learned avoidance response. In order to investigate the impact of experience with noxious stimuli in one conditioning context on learning and memory performance in a separate, non-aversively motivated task, juvenile recognition ability was examined in adult female rats exposed previously to one of two environmental stressors. In particular, experimental adult rats were either socially defeated by exposure to an aggressive conspecific rat or fear conditioned using single or multiple pairings with footshock prior to performance of the social recognition task. Experiment 1 established that repeated exposure to a single juvenile resulted in social memory formation reflected in decreased social investigation from the first to the second exposure. Experiment 2 documented that both single and multiple pairings of an environment with footshock produced robust freezing behavior (90-95% suppression of activity). In addition, fear conditioning produced a non-specific 5-60% increase in social investigation time in both single and multiple-pairing fear conditioned groups which confounded the ability of the social recognition measure to assess effects of fear conditioning on learning and memory performance per se. In contrast, Experiment 3 documented that when social recognition memory performance was impaired to 85% of control levels by imposition of a 2 h delay, exposure to a social defeat stressor reinstated optimal social recognition memory performance. These findings suggest that the after effects of fear conditioning include non-specific alteration of social investigation whereas exposure to conspecific aggression enhances subsequent social recognition memory.     

Learning orthography in adulthood: A magnetoencephalographic study

Previous work demonstrated that there were differences between literate and comparable illiterate adult subjects. These differences were found in the performance on several tests and on patterns of activation on PET and fMRI. In the present study subjects that learned to read and to write in adulthood (being previously completely illiterate) were compared to controls, that is subjects that learned at school at the proper age. Magnetoencephalography was done while subjects were reading words. Results showed that, although the reading performance was the same in both groups while performing the task, the pattern of source distribution was different between groups. There were more late sources in right temporo‐parietal areas of late literates compared to controls and more late sources in left inferior frontal cortex in control subjects. It is concluded that learning to read in adulthood is a process supported by different brain structures from the ones used when learning occurs at the proper age. This may suggest that the same task can be similarly performed by relying on diverse functional brain anatomic networks.     

Snoddy (1926) revisited: time scales of motor learning

The authors investigated the time scales of the learning of a mirror-tracing task to reexamine G. S. Snoddy's (1926) original claim and the received theoretical view (A. Newell & P. S. Rosenbloom, 1981) that motor learning follows a power law. Adult participants (N = 16) learned the tracing task in either a normal or a reversed visual-image condition over 5 consecutive days of practice and then performed 1 day of practice 1 week later and again 1 month later. The reversed-image group's performance was poorer than that of the normal-image group throughout the practice. An exponential was the best fitting function on individual data, but the power-law function was the best fit on the group-averaged data. The findings provided preliminary evidence that 2 characteristic time scales, (a) fast, dominated by warm-up, and (b) slow, dominated by persistent change, capture individuals' performance in the learning of the mirror-tracing task.     

A unified model for perceptual learning

Perceptual learning in adult humans and animals refers to improvements in sensory abilities after training. These improvements had been thought to occur only when attention is focused on the stimuli to be learned (task-relevant learning) but recent studies demonstrate performance improvements outside the focus of attention (task-irrelevant learning). Here, we propose a unified model that explains both task-relevant and task-irrelevant learning. The model suggests that long-term sensitivity enhancements to task-relevant or irrelevant stimuli occur as a result of timely interactions between diffused signals triggered by task performance and signals produced by stimulus presentation. The proposed mechanism uses multiple attentional and reinforcement systems that rely on different underlying neuromodulators. Our model provides insights into how neural modulators, attentional and reinforcement learning systems are related.     

Persistence of chronic nicotine-induced cognitive facilitation.

Nicotine has been found in a variety of species and behavioral paradigms to improve memory performance. The beneficial effect of nicotine has been seen after both acute and chronic administration. Interestingly, improved performance has been seen 24 h after acute injection and for at least 2 weeks after chronic administration. However, it is not clear from previous studies whether the persistence of the improved performance represents a true carryover of the drug effect or is due to the behavioral experience while under nicotine's effect. The current study was conducted to determine whether the facilitating effect of nicotine on learning and memory performance could be seen after withdrawal even if there was no behavioral training during the period of chronic nicotine administration. Rats were administered nicotine chronically for 3 weeks but were not tested during that time. Starting 1 week after withdrawal they were trained on a working memory paradigm in an eight-arm radial maze. The nicotine-treated rats started out at control-like levels of performance, but showed significantly faster learning as detected by three different measures of choice accuracy. By the final phase of testing the control subjects had caught up with the nicotine-treated rats. After the acquisition phase, acute challenges with the nicotinic and muscarinic antagonists, mecamylamine and scopolamine, did not elicit any differential effects in the nicotine-treated and control groups. The current study demonstrated that nicotine-induced cognitive facilitation persists for at least 4 weeks after withdrawal and does not depend upon behavioral test experience under the influence of the drug. The mechanism for this persisting effect is not currently understood.(ABSTRACT TRUNCATED AT 250 WORDS)     

A maturation effect in response inhibition in the rat

The finding that there are maturational differences between the ability to learn and to perform a task requiring young Wistar rats to inhibit a response was examined. Using an operant task, different from that employed in the previous studies, it was established that the finding was not task specific. The relative contribution of different periods in the early training stage to later savings in learning was also examined. It was confirmed that there is an early performance deficit by weanling rats on tasks requiring them to inhibit a previously learned response in the presence of a discriminative cue. Rats given early training on the task during this period of performance deficit nevertheless showed significant savings in later learning of the task, indicating that they had learned as much in that stage as they would have if given the same training at an age when performance is at the adult level. It was revealed that despite age-related differences in performance it was not so much the age at which early training took place as the amount of training given that affected later savings. The results are discussed in light of evidence of similar differences between the learning and performance of discrimination tasks exhibited by young children.     

Reducing the gap in numerical knowledge between low- and middle-income preschoolers

We compared the learning from playing a linear number board game of preschoolers from middle-income backgrounds to the learning of preschoolers from low-income backgrounds. Playing this game produced greater learning by both groups than engaging in other numerical activities for the same amount of time. The benefits were present on number line estimation, magnitude comparison, numeral identification, and arithmetic learning. Children with less initial knowledge generally learned more, and children from low-income backgrounds learned at least as much, and on several measures more, than preschoolers from middle-income backgrounds with comparable initial knowledge. The findings suggest a class of intervention that might be especially effective for reducing the gap between low-income and middle-income children's knowledge when they enter school.     

Learning categories by making predictions: An investigation of indirect category learning

Categories are learned in many ways, but studies of category learning have generally focused on classification learning. This focus may limit the understanding of categorization processes. Two experiments were conducted in which participants learned categories of animals by predicting how much food each animal would eat. We refer to this as indirect category learning, because the task andthe feedback were not directly related to category membership, yet category learning was necessary for good performance in the task. In the first experiment, we compared the performance of participants who learned the categories indirectly with the performance of participants who first learned to classify the objects. In the second experiment, we replicated the basic findings and examined attention to different features during the learning task. In both experiments, participants who learned in the prediction-only condition displayed a broader distribution of attention than participants who learned in the classification-and-prediction condition did. Some participants in the prediction-only group learned the family resemblance structure of the categories, even when a perfect criterial attribute was present. In contrast, participants who first learned to classify the objects tended to learn the criterial attribute.     

Do learned irrelevance and perseveration play a role during discrimination learning?

In both healthy participants and various patient populations, performance on attentional set-shifting tasks has been found to be affected by learned irrelevance and/or perseveration. The present study examined whether or not these processes also play a role during the initial discrimination learning phase of those tasks. To this end, participants first solved a multidimensional discrimination learning task. Thereafter, they underwent three types of shift of relevant and/or irrelevant stimulus attributes, which enabled the assessment of the separate contribution of perseveration and learned irrelevance to post-shift task performance. Subsequent correlational analyses revealed that the number of errors during initial discrimination learning was significantly correlated with the number of errors in the learned irrelevance-shift but not the perseveration-shift. This suggests that processes underlying learned irrelevance in post-shift task performance also play a significant role during initial discrimination learning. The implications of these results for interpreting deficits in shifting are discussed.     

Visual discrimination learning and strategy behavior in the fat-tailed dunnart (Sminthopsis crassicaudata)

Fat-tailed dunnarts (Sminthopsis crassicaudata) were trained on visual discrimination learning-set, reversal-set, and spatial delayed-alternation tasks. The learning set involved 36 2-way black-and-white pattern discriminations and 5 probe reversals. Ten reversals of a black-and-white pattern discrimination were followed by 5 novel tasks. Spatial alternation was tested at delays up to 20 s. Learning-set and reversal-set formation, including 1-trial learning and spontaneous transfer from learning set to reversals and vice versa, was found. Learning-set-experienced dunnarts showed no retention of previously learned tasks 1 week after testing but demonstrated consistently high Trial 2 performance, indicating the retention of a response strategy. Delayed-alternation tasks were learned up to 10-s delays. These results provide the first evidence of a visually guided "win-stay, lose-shift" strategy in a marsupial.     

Declarative strategies persist under increased cognitive load

When humans simultaneously execute multiple tasks, performance on individual tasks suffers. Complementing existing theories, this article poses a novel question to investigate interactions between memory systems supporting multi-tasking performance: When a primary and dual task both recruit declarative learning and memory systems, does simultaneous performance of both tasks impair primary task performance because learning in the declarative system is reduced, or because control of the primary task is passed to slower procedural systems? To address this question, participants were trained on either a perceptual categorization task believed to rely on procedural learning or one of three different categorization tasks believed to rely on declarative learning. Task performance was examined with and without a simultaneous dual task thought to recruit working memory and executive attention. To test whether the categories were learned procedurally or declaratively, the response keys were switched after a learning criterion had been reached. Large impairments in performance after switching the response keys are taken to indicate procedural learning, and small impairments are taken to indicate declarative learning. Our results suggest that the declarative memory categorization tasks (regardless of task difficulty) were learned by declarative systems, regardless of whether they were learned under dual-task conditions.