Associative learning

The vertebrate brain continues to produce new neurons throughout life. In the rat hippocampus, several thousand are produced each day, many of which die within weeks. Associative learning can enhance their survival; however, until now it was unknown whether new neurons are involved in memory formation. Here we show that a substantial reduction in the number of newly generated neurons in the adult rat impairs hippocampal-dependent trace conditioning, a task in which an animal must associate stimuli that are separated in time. A similar reduction did not affect learning when the same stimuli are not separated in time, a task that is hippocampal-independent. The reduction in neurogenesis did not induce death of mature hippocampal neurons or permanently alter neurophysiological properties of the CA1 region, such as long-term potentiation. Moreover, recovery of cell production was associated with the ability to acquire trace memories. These results indicate that newly generated neurons i...

The authors present a Bayesian framework for understanding how adults and children learn the meanings of words. The theory explains how learners can generalize meaningfully from just one or a few positive examples of a novel word's referents, by making rational inductive inferences that integrate prior knowledge about plausible word meanings with the statistical structure of the observed examples. The theory addresses shortcomings of the two best known approaches to modeling word learning, based on deductive hypothesis elimination and associative learning. Three experiments with adults and children test the Bayesian account's predictions in the context of learning words for object categories at multiple levels of a taxonomic hierarchy. Results provide strong support for the Bayesian account over competing accounts, in terms of both quantitative model fits and the ability to explain important qualitative phenomena. Several extensions of the basic theory are discussed, illustrating the broader potential for Bayesian models of word learning.

Reinforcement learning is bedeviled by the curse of dimensionality: the number of parameters to be learned grows exponentially with the size of any compact encoding of a state. Recent attempts to combat the curse of dimensionality have turned to principled ways of exploiting temporal abstraction, where decisions are not required at each step, but rather invoke the execution of temporally-extended activities which follow their own policies until termination. This leads naturally to hierarchical control architectures and associated learning algorithms. We review several approaches to temporal abstraction and hierarchical organization that machine learning researchers have recently developed. Common to these approaches is a reliance on the theory of semi-Markov decision processes, which we emphasize in our review. We then discuss extensions of these ideas to concurrent activities, multiagent coordination, and hierarchical memory for addressing partial observability.

Our decisions are guided by information learnt from our environment. This information may come via personal experiences of reward, but also from the behaviour of social partners. Social learning is widely held to be distinct from other forms of learning in its mechanism and neural implementation; it is often assumed to compete with simpler mechanisms, such as reward-based associative learning, to drive behaviour. Recently, neural signals have been observed during social exchange reminiscent of signals seen in studies of associative learning. Here we demonstrate that social information may be acquired using the same associative processes assumed to underlie reward-based learning. We find that key computational variables for learning in the social and reward domains are processed in a similar fashion, but in parallel neural processing streams. Two neighbouring divisions of the anterior cingulate cortex were central to learning about social and reward-based information, and for determining the extent to which each source of information guides behaviour. When making a decision, however, the information learnt using these parallel streams was combined within ventromedial prefrontal cortex. These findings suggest that human social valuation can be realized by means of the same associative processes previously established for learning other, simpler, features of the environment.

The main aim of the paper is to present an up-to-date computational theory of hippocampal function and the predictions it makes about the different subregions (dentate gyrus, CA3 and CA1), and to examine behavioral and electrophysiological data that address the functions of the hippocampus and particularly its subregions. Based on the computational proposal that the dentate gyrus produces sparse representations by competitive learning and via the mossy fiber pathway forces new representations on the CA3 during learning (encoding), it has been shown behaviorally that the dentate gyrus supports spatial pattern separation during learning. Based on the computational proposal that CA3-CA3 autoassociative networks are important for episodic memory, it has been shown behaviorally that the CA3 supports spatial rapid one-trial learning, learning of arbitrary associations where space is a component, pattern completion, spatial short-term memory, and sequence learning by associations formed between successive items. The concept that the CA1 recodes information from CA3 and sets up associatively learned backprojections to neocortex to allow subsequent retrieval of information to neocortex, is consistent with findings on consolidation. Behaviorally, the CA1 is implicated in processing temporal information as shown by investigations requiring temporal order pattern separation and associations across time; computationally this could involve temporal decay memory, and temporal sequence memory which might also require CA3. The perforant path input to DG is implicated in learning, to CA3 in retrieval from CA3, and to CA1 in retrieval after longer time intervals (''intermediate-term memory''). #

A group of ten patients with idiopathic Parkinson's disease (PD) was tested on a series of automated tests of learning, memory, planning and attention whilst either on or offl-dopa medication. Controlled with-drawal ofl-dopa interfered with aspects of performance on three of the tests that had previously been shown to be sensitive to frontal lobe dysfunction; a spatial working memory task, the Tower of London planning test, and a visual discrimination paradigm that also included intra- and extra-dimensional shift tests of selective attention. More specifically, errors were increased in the spatial working memory test, and both the accuracy and latency of thinking were impaired. Thinking time was significantly slowed followingl-dopa withdrawal, even though the possible contaminating effects on motor slowing were fully controlled by a yoked control procedure. Nine out of ten patients reached a further stage of the visual discrimination, set-shifting paradigm when on, rather than off,l-dopa medication. Spatial span was also impaired off medication, but there were no effects ofl-dopa withdrawal on tests of pattern and spatial recognition memory, simultaneous and delayed matching to sample or visuospatial conditional associative learning. Comparisons with a large control group confirmed previous findings that PD is associated with deficits on the majority of these tests. The results are discussed in terms of the fronto-striatal, dopamine dependent nature of some of the cognitive deficits found in PD, but the apparent dopamine-independent nature of deficits in other aspects of cognitive functioning, notably in tests of visual recognition memory and associative learning.

CITATIONS 353 READS 43 3 authors: Some of the authors of this publication are also working on these related projects: Synchrony of beta oscillations in the frontoparietal network View project Category representations in parietal and prefrontal cortex on different levels of category abstractness

Three groups of neurosurgical patients with temporal lobe excisions, frontal lobe excisions or unilateral amygdalo-hippocampectomy were assessed on a computerized battery of tasks designed to investigate visuo-spatial short-term recognition memory and learning. A double dissociation is reported between deficits of pattern recognition memory and spatial recognition memory which were observed in the two posterior groups and frontal lobe patients, respectively. In addition, both the temporal lobe and amygdalo-hippocampectomy patients were also impaired on a delayed matchingto-sample paradigm whilst frontal lobe patients performed at an equivalent level to controls. Finally, whilst the impaired performance of the three groups was indistinguishable on a test of pairedassociate learning, quite different patterns of deficit were observed on a test of spatial workiny memory. These results are discussed with reference to recent suggestions that visual recognition memory is mediated by a neural system which includes, as major components, the inferotemporal cortex, the medial temporal lobe structures and particular sectors of the frontal lobe, and are compared to previous findings from patients with idiopathic Parkinson's disease and dementia of the Alzheimer type.

Behavioral ecologists and economists emphasize that potential costs, as well as rewards, influence decision making. Although neuroscientists assume that frontal areas are central to decision making, the evidence is contradictory and the critical region remains unclear. Here it is shown that frontal lobe contributions to cost-benefit decision making can be understood by positing the existence of two independent systems that make decisions about delay and effort costs. Anterior cingulate cortex lesions affected how much effort rats decided to invest for rewards. Orbitofrontal cortical lesions affected how long rats decided to wait for rewards. The pattern of disruption suggested the deficit could be related to impaired associative learning. Impairments of the two systems may underlie apathetic and impulsive choice patterns in neurological and psychiatric illnesses. Although the existence of two systems is not predicted by economic accounts of decision making, our results suggest that delay and effort may exert distinct influences on decision making.

Imitation poses a unique problem: how does the imitator know what pattern of motor activation will make their action look like that of the model? Specialist theories suggest that this correspondence problem has a unique solution; there are functional and neurological mechanisms dedicated to controlling imitation. Generalist theories propose that the problem is solved by general mechanisms of associative learning and action control. Recent research in cognitive neuroscience, stimulated by the discovery of mirror neurons, supports generalist solutions. Imitation is based on the automatic activation of motor representations by movement observation. These externally triggered motor representations are then used to reproduce the observed behaviour. This imitative capacity depends on learned perceptual-motor links. Finally, mechanisms distinguishing self from other are implicated in the inhibition of imitative behaviour.

In a classical conditioning procedure, honeybees associate an odor with sucrose resulting in the capacity of the odor to evoke an appetitive response, the extension of the proboscis (PER). Here, we study the effects of pairing an odor with injections of octopamine (OA) as a substitute for sucrose into three putative brain sites of odor/sucrose convergence. OA injected into the mushroom body (MB) calyces or the antennal lobe but not the lateral protocerebral lobe produces a lasting, pairing-specific enhancement of PER. During pairings, OA injected into the MB calyces results in an additional pairing-specific effect, because it does not lead to an acquisition but a consolidation after conditioning. These results suggest that the neuromodulator OA has the capacity of inducing associative learning in an insect brain. Moreover, they suggest the antennal lobes and the calyces as at least partially independent sites of associating odors that may contribute differently to learning and memor...

The orbitofrontal cortex (OFC) is crucial for changing established behaviour in the face of unexpected outcomes. This function has been attributed to the role of the OFC in response inhibition or to the idea that the OFC is a rapidly flexible associative-learning area. However, recent data contradict these accounts, and instead suggest that the OFC is crucial for signalling outcome expectancies. We suggest that this function -signalling of expected outcomes -can also explain the crucial role of the OFC in changing behaviour in the face of unexpected outcomes.

To determine general or species-specific properties in neural systems, it is necessary to use comparative data in evaluating experimental findings. Presented here are data on associative learning and memory formation in honeybees, emphasizing a comparative approach. We focus on four aspects: (1) the role of an identified neuron, VUM mx1 , as a neural substrate of appetitive reinforcement; (2) the sequences of molecular events as they correlate with five forms of memory stages; (3) the localization of the memory traces following appetitive olfactory learning; and (4) the brief description of several forms of complex learning in bees (configuration in olfactory conditioning, categorization in visual feature learning, delayed matching-to-sample learning, and latent learning in navigation). VUM mx1 activity following the conditioned stimulus odor is sufficient to replace the unconditioned stimulus, and VUM mx1 changes its response properties during learning similarly to what is known from dopamine neurons in the basal ganglia of the mammalian brain. The transition from short-to mid-and long-term forms of memory can be related to specific activation of second messenger cascades (involving NOS, PKA, PKC, and PKM) resembling general features of neural plasticity at the cellular level. The particular time course of the various memory traces may be adapted to the behavioral context in which they are used; here, the foraging cycle of the bee. Memory traces for even such a simple form of learning as olfactory conditioning are multiple and distributed, involving first-and second-order sensory neuropils (antennal lobe and mushroom bodies), but with distinctly different properties. The wealth of complex forms of learning in the context of foraging indicates basic cognitive capacities based on rule extraction and context-dependent learning. It is believed that bees might be a useful model for studying cognitive faculties at a middle level of complexity.

Abstract Rationale. Modafinil, a novel wake-promoting agent, has been shown to have a similar clinical profile to that of conventional stimulants such as methylphenidate. We were therefore interested in assessing whether modafinil, with its unique pharmacological mode of action, might offer similar potential as a cognitive enhancer, without the side effects commonly experienced with amphetamine-like drugs. Objectives. The main aim of this study was to evaluate the cognitive enhancing potential of this novel agent using a comprehensive battery of neuropsychological tests. Methods. Sixty healthy young adult male volunteers received either a single oral dose of placebo, or 100 mg or 200 mg modafinil prior to performing a variety of tasks designed to test memory and attention. A randomised double-blind, between-subjects design was used. Results. Modafinil significantly enhanced performance on tests of digit span, visual pattern recognition memory, spatial planning and stop-signal reaction time. These performance improvements were complemented by a slowing in latency on three tests: delayed matching to sample, a decision-making task and the spatial planning task. Subjects reported feeling more alert, attentive and energetic on drug. The effects were not clearly dose dependent, except for those seen with the stop-signal paradigm. In contrast to previous findings with methylphenidate, there were no significant effects of drug on spatial memory span, spatial working memory, rapid visual information processing or attentional set-shifting. Additionally, no effects on paired associates learning were identified. Conclusions. These data indicate that modafinil selectively improves neuropsychological task performance. This improvement may be attributable to an enhanced ability to inhibit pre-potent responses. This effect appears to reduce impulsive responding, suggesting that modafinil may be of benefit in the treatment of attention deficit hyperactivity disorder.

Long-term depression (LTD) of the synapse formed between cortical pyramidal neurons and striatal medium spiny neurons is central to many theories of motor plasticity and associative learning. The induction of LTD at this synapse is thought to depend upon D 2 dopamine receptors localized in the postsynaptic membrane. If this were true, LTD should be inducible in neurons from only one of the two projection systems of the striatum. Using transgenic mice in which neurons that contribute to these two systems are labeled, we show that this is not the case. Rather, in both cell types, the D 2 receptor dependence of LTD induction reflects the need to lower M 1 muscarinic receptor activity-a goal accomplished by D 2 receptors on cholinergic interneurons. In addition to reconciling discordant tracts of the striatal literature, these findings point to cholinergic interneurons as key mediators of dopamine-dependent striatal plasticity and learning.

In 5 experiments, the authors examined the development of automatic response inhibition in the go/no-go paradigm and a modified version of the stop-signal paradigm. They hypothesized that automatic response inhibition may develop over practice when stimuli are consistently associated with stopping. All 5 experiments consisted of a training phase and a test phase in which the stimulus mapping was reversed for a subset of the stimuli. Consistent with the automatic-inhibition hypothesis, the authors found that responding in the test phase was slowed when the stimulus had been consistently associated with stopping in the training phase. In addition, they found that response inhibition benefited from consistent stimulus-stop associations. These findings suggest that response inhibition may rely on the retrieval of stimulus-stop associations after practice with consistent stimulus-stop mappings. Stimulus-stop mapping is typically consistent in the go/no-go paradigm, so automatic inhibitio...

The heterogeneity of ␥-aminobutyric acid type A (GABAA) receptors contributes to the diversity of neuronal inhibition in the regulation of information processing. Although most GABA A receptors are located synaptically, the small population of ␣5GABAA receptors is largely expressed extrasynaptically. To clarify the role of the ␣5GABAA receptors in the control of behavior, a histidineto-arginine point mutation was introduced in position 105 of the murine ␣5 subunit gene, which rendered the ␣5GABAA receptors diazepam-insensitive. Apart from an incomplete muscle relaxing effect, neither the sedative, anticonvulsant, nor anxiolytic-like activity of diazepam was impaired in ␣5(H105R) mice. However, in hippocampal pyramidal cells, the point mutation resulted in a selective reduction of ␣5GABAA receptors, which altered the drugindependent behavior. In line with the role of the hippocampus in certain forms of associative learning, trace fear conditioning, but not delay conditioning or contextual conditioning, was facilitated in the mutant mice. Trace fear conditioning differs from delay conditioning in that the conditioned and unconditioned stimulus are separated by a time interval. Thus, the largely extrasynaptic ␣5GABAA receptors in hippocampal pyramidal cells are implicated as control elements of the temporal association of threat cues in trace fear conditioning.

As one of the most extensively studied protein hormones, insulin and its receptor have been known to play key roles in a variety of important biological functions. Until recent years, the functions of insulin and insulin receptor (IR) in the central nervous system (CNS) have largely remained unclear. IR is abundantly expressed in several specific brain regions that govern fundamental behaviors such as food intake, reproduction and high cognition. The IR from the periphery and CNS exhibit differences in both structure and function. In addition to that from the peripheral system, locally synthesized insulin in the brain has also been identified. Accumulated evidence has demonstrated that insulin/IR plays important roles in associative learning, as suggested by results from both interventive and correlative studies. Interruption of insulin production and IR activity causes deficits in learning and memory formation. Abnormal insulin/IR levels and activities are seen in Alzheimer's dementia, whereas administration of insulin significantly improves the cognitive performance of these patients. The synaptic bases for the action of insulin/IR include modifying neurotransmitter release processes at various types of presynaptic terminals and modulating the activities of both excitatory and inhibitory postsynaptic receptors such as NMDA and GABA receptors, respectively. At the molecular level, insulin/IR participates in regulation of learning and memory via activation of specific signaling pathways, one of which is shown to be associated with the formation of long-term memory and is composed of intracellular molecules including the shc, Grb-r/SOS, Ras/Raf, and MEK/MAP kinases. Cross-talk with another IR pathway involving IRS1, PI3 kinase, and protein kinase C, as well as with the non-receptor tyrosine kinase pp60c-src, may also be associated with memory processing.

26 Menard, M.T. et al. (1996) Encoding words and pictures: a positron emission tomography study Neuropsychologia 34,[185][186][187][188][189][190][191][192][193][194] 27 Puce, A. et al. (1996) Differential sensitivity of human visual cortex to faces, letterstrings and textures: a functional magnetic resonance imaging study J. Neurosci. 16,[5205][5206][5207][5208][5209][5210][5211][5212][5213][5214][5215] 28 Sergent, J., Ohta, S. and MacDonald, B. (1992) Functional neuroanatomy of face and object processing: a positron emission tomography study Brain 115, 15-36 29 Sergent, J. et al. (1992) Positron emission tomography study of letter and object processing: empirical findings and methodological considerations Cereb. Cortex 2, 68-80 30 Kosslyn, S.M. et al. (1994) Identifying objects seen from different viewpoints: a PET investigation Brain 117, 1055-1071 31 Kosslyn, S.M., Alpert, N.M. and Thompson, W.L. (1995) Identifying objects at different levels of hierarchy: a positron emission tomography study Hum. Brain Mapp. 3, 107-132 32 Malach, R. et al. (1995) Object-related activity revealed by functional magnetic resonance imaging in human occipital cortex Proc. Natl. Acad. Sci. U. S. A. 92, 8135-8139 33 Kanwisher, N. et al. (1997) A locus in human extrastriate cortex for visual shape analysis J. Cogn. Neurosci. 9, 133-142 34 Haxby, J.V. et al. (1994) The functional organization of human exstrastriate cortex: a PET-rCBF study of selective attention to faces and locations J. Neurosci. 14, 6336-6353 35 Haxby, J.V. et al. (1996) Face encoding and recognition in the human brain Proc. Natl. Acad. Sci. U. S. A. 93, 922-927 F a r a h & A g u i r r e -I m a g i n g v i s u a l r e c o g n i t i o n The role of the hippocampal formation in learning and memory has long been recognized. However, despite decades of intensive research, the neurobiological basis of this process in the hippocampus remains enigmatic. Over 30 years ago, the production of new neurons was found to occur in the brains of adult rodents. More recently, the documentation of adult neurogenesis in the hippocampal formation of a variety of mammals, including humans, has suggested a novel approach towards understanding the biological bases of hippocampal function. Contemporary theories of hippocampal function include an important role for this brain region in associative learning. The addition of new neurons and consequently, their novel contribution to hippocampal circuitry could conceivably be a mechanism for relating spatially or temporally disparate events. In this review, we examine several lines of evidence suggesting that adult-generated neurons are involved in hippocampal-dependent learning. In particular, we examine the variables that modulate hippocampal neurogenesis in adulthood and their relation to learning and memory.

Equipped with a mini brain smaller than one cubic millimeter and containing only 950,000 neurons, honeybees could be indeed considered as having rather limited cognitive abilities. However, bees display a rich and interesting behavioral repertoire, in which learning and memory play a fundamental role in the framework of foraging activities. We focus on the question of whether adaptive behavior in honeybees exceeds simple forms of learning and whether the neural mechanisms of complex learning can be unraveled by studying the honeybee brain. Besides elemental forms of learning, in which bees learn speciWc and univocal links between events in their environment, bees also master diVerent forms of non-elemental learning, including categorization, contextual learning and rule abstraction, both in the visual and in the olfactory domain. DiVerent protocols allow accessing the neural substrates of some of these learning forms and understanding how complex problem solving can be achieved by a relatively simple neural architecture. These results underline the enormous richness of experiencedependent behavior in honeybees, its high Xexibility, and the fact that it is possible to formalize and characterize in controlled laboratory protocols basic and higher-order cognitive processing using an insect as a model.

Time-dependent, learning-related changes in hippocampal excitability were evaluated by recording from rabbit CA1 pyramidal neurons in slices prepared at various times after acquisition of trace eyeblink conditioning. Increased excitability (reduced postburst afterhyperpolarizations and reduced spike-frequency adaptation) was seen as early as 1 hr after acquisition to behavioral criterion, was maximal in neurons studied 24 hr later, and returned to baseline within 7 d, whereas behavioral performance remained asymptotic for months. Neurons were held at -67 mV to equate voltage-dependent effects. No learning-related effects were observed on input resistance, action-potential amplitude or duration, or resting membrane potential. The excitability changes were learning-specific, because they were not seen in neurons from very slow learning (exhibited < 30% conditioned responses after 15 training sessions) or from pseudoconditioned control rabbits. Neurons from rabbits that displayed as...

Dendritic spines are sources of synaptic contact that can be altered by experience and, as such, may be involved in memories for that experience. Here we tested whether the acquisition of new memories is associated with changes in the density of dendritic spines. Adult male rats were trained using the trace eyeblink conditioning paradigm, an associative learning task that requires the hippocampus for acquisition. Additional groups were exposed to the same number of stimuli presented in an explicitly unpaired manner or were naive. Twenty-four hours later, the density of dendritic spines was measured using Golgi impregnation. Trace conditioning was associated with an increase in the density of dendritic spines on the pyramidal cells of area CA1 of the hippocampus, an effect that was prevented by blocking acquisition of the learned response with a competitive NMDA receptor antagonist. Training with delay conditioning, a similar task that does not require the hippocampus, also produced ...

AND CONCLUSIONS 1. The orbitofrontal cortex is implicated in the rapid learning of new associations between visual stimuli and primary reinforcers such as taste. It is also the site of convergence of information from olfactory, gustatory, and visual modalities. To investigate the neuronal mechanisms underlying the formation of odor-taste associations, we made recordings from olfactory neurons in the orbitofrontal cortex during the performance of an olfactory discrimination task and its reversal in macaques.

From beverages to consumer electronics, marketers are using color in innovative ways. Despite this, little academic research has investigated the role that color plays in marketing. This paper examines how color affects consumer perceptions through a series of four studies. The authors provide a framework and empirical evidence that draws on research in aesthetics, color psychology, and associative learning to map hues onto brand personality dimensions (Study 1), as well as examine the roles of saturation and value for amplifying brand personality traits (Study 2). The authors also demonstrate how marketers can strategically use color to alter brand personality and purchase intent (Study 3), and how color influences the likability and familiarity of a brand (Study 4). The results underscore the importance of recognizing the impact of color in forming consumer brand perceptions.

Although many psychopharmacological factors contribute to nicotine addiction, midbrain dopaminergic systems have received much attention because of their roles in reinforcement and associative learning. It is generally thought that the mesocorticolimbic dopaminergic system is important for the acquisition of behaviors that are reinforced by the salient drives of the environment or by the inappropriate stimuli of addictive drugs. Nicotine, as obtained from tobacco, can activate nicotinic acetylcholine receptors (nAChRs) and excite midbrain neurons of the mesocorticolimbic system. Using midbrain slices from rats, wild-type mice, and genetically engineered mice, we have found differences in the nAChR currents from the ventral tegmental area (VTA) and the substantia nigra compacta (SNc). Nicotinic AChRs containing the alpha7 subunit (alpha7* nAChRs) have a low expression density. Electrophysiological analysis of nAChR currents, autoradiography of [125I]-alpha-bungarotoxin binding, and i...

Some researchers have suggested that although feedback may enhance performance during associative learning, it does so at the expense of later retention. To examine this issue, subjects (N = 258) learned Luganda-English word pairs. After 2 initial exposures to the materials, subjects were tested on each item several times, with the presence and type of feedback varying between subjects. A final test followed after I week. Supplying the correct answer after an incorrect response not only improved performance during the initial learning session-it also increased final retention by 494%. On the other hand, feedback after correct responses made little difference either immediately or at a delay, regardless of whether the subject was confident in the response. Practical and theoretical implications are discussed.

When subjects switch between a pair of stimulus-response tasks, reaction time is slower on trial N if a different task was performed on trial N Ϫ 1. We present a parallel distributed processing (PDP) model that simulates this effect when subjects switch between word reading and color naming in response to Stroop stimuli. Reaction time on ''switch trials'' can be slowed by an extended response selection process which results from (a) persisting, inappropriate states of activation and inhibition of task-controlling representations; and (b) associative learning, which allows stimuli to evoke tasks sets with which they have recently been associated (as proposed by . The model provides a good fit to a large body of empirical data, including findings which have been seen as problematic for this explanation of switch costs, and shows similar behavior when the parameters are set to random values, supporting Allport and Wylie's proposal.

Can direct change in state of consciousness through specific mental techniques extend human life and reverse age-related declines? To address this question, 73 residents of 8 homes for the elderly (mean age = 81 years) were randomly assigned among no treatment and 3 treatments highly similar in external structure and expectations: the Transcendental Meditation (TM) program, mindfulness training (MF) in active distinction making, or a relaxation (low mindfulness) program. A planned comparison indicated that the "restful alert" TM group improved most, followed by MF, in contrast to relaxation and no-treatment groups, on paired associate learning; 2 measures of cognitive flexibility; mental health; systolic blood pressure; and ratings of behavioral flexibility, aging, and treatment efficacy. The MF group improved most, followed by TM, on perceived control and word fluency. After 3 years, survival rate was 100% for TM and 87.5% for MF in contrast to lower rates for other groups.

Mental imagery improves paired-associate (PA) learning relative to overt rehearsal. The effect might be due to increased reliability of stimulus encoding or to increased relational association produced by imagery. These hypotheses expect different outcomes when imagery and ...

Current etiological models of anxiety disorders emphasize both internal diatheses, or risk factors, and external stressors as important in the development and maintenance of clinical anxiety. Although considerable evidence suggests personality, genetic, and environmental variables are important to these diathesis-stress interactions, this general approach could be greatly enriched by incorporating recent developments in experimental research on fear and anxiety learning. In this article, we attempt to integrate the experimental literature on fear/anxiety learning and the psychopathology literature on clinical anxiety, identify areas of inconsistency, and recommend directions for future research. First, we provide an overview of contemporary models of anxiety disorders involving fear/anxiety learning. Next, we review the literature on individual differences in associative learning among anxious and non-anxious individuals. We also examine additional possible sources of individual differences in the learning of both fear and anxiety, and indicate where possible parallels may be drawn. Finally, we discuss recent developments in basic experimental research on fear conditioning and anxiety, with particular attention to research on contextual learning, and indicate the relevance of these findings to anxiety disorders.

The effects of perirhinal (Prh) and fornix (Fx) lesions were compared on a series of spatial and nonspatial memory tests. These tests included delayed nonmatching-to-position in an operant chamber, a spatial (lever) discrimination and its subsequent reversals, delayed spatial alternation in a T-maze, and an object recognition memory test using both normal objects and 're configured' objects. As expected, the rats with fornix lesions were impaired on all of the spatial tests. Their performance on the recognition test was, however, left intact. The perirhinal lesions produced a quite different pattern of results. Animals with these lesions were unimpaired on all three spatial tasks, but displayed evidence of an impairment on the object recognition test. This impairment was restricted to the longer delay (15 rain) and was only found with the normal objects. These findings suggest that the actions of the perirhinal cortex and the hippocampus can be dissociated from one another.

Seabird chicks respond to food shortages by increasing corticosterone (cort) secretion, which is probably associated with fitness benefits and costs. To examine this, we experimentally increased levels of circulating cort in captive black-legged kittiwake chicks fed ad libitum. We found that cort-implanted chicks begged more frequently and were more aggressive compared to controls. These behavioral modifications must be beneficial to chicks as they facilitate acquisition of food from the parents and might trigger brood reduction and reduced competition for food. Cort-implanted chicks also increased food intake; however, their growth rates were similar to controls. To examine the costs of chronically increased circulating levels of cort, we removed cort implants and, after a 10-day recovery period, tested cognitive abilities of young kittiwakes. We found that the ability of kittiwakes to associate a visual cue with the presence of food in a choice situation was compromised by the experimental elevation of cort during development. To examine the long-term costs of increased levels of cort, 8 months later we tested the performance of the same individuals in a spatial task requiring them to make a detour around a barrier in order to escape from an enclosure. Individuals treated with cort during development took significantly more time to solve this task compared to controls. The results of this study suggest that the adrenocortical response of a developing bird to environmental stressors is associated with both benefits (increased food intake, foraging behavior, and aggression) and costs (low growth efficiency and compromised cognitive abilities later in life). This provides an evolutionary framework for relating juvenile physiological traits to fitness of birds in subsequent life-history stages.

showed that adults were able to segment into words an artificial language that included no pauses or other prosodic cues for word boundaries. We propose an account of their results that requires only limited computational abilities and memory capacity. In this account, parsing emerges as a natural consequence of the on-line attentional processing of the input, thanks to basic laws of memory and associative learning. Our account was implemented in a computer program, PARSER. Simulations revealed that PARSER extracted the words of the language well before exhausting the material presented to participants in the Saffran et al. experiments. In addition, PARSER was able to simulate the results obtained under attention-disturbing conditions (Saffran, Newport, Aslin, Tunick, & Barrueco, 1997) and those collected from 8-month-old infants . Finally, the good performance of PARSER was not limited to the trisyllabic words used by Saffran et al., but also extended to a language composed of one-to five-syllable words.

The results of a previous study have suggested that impaired performance on one neuropsychological test, CANTAB Paired Associates Learning (PAL), may serve as a marker for preclinical Alzheimer's disease (AD). In a group of individuals with 'questionable dementia', the baseline PAL performance was found to correlate significantly with subsequent deterioration in global cognitive function over an 8-month period. The present paper reports diagnostic outcome data for the same individuals 32 months after the first assessment and evaluates the predictive diagnostic utility of baseline neuropsychological measures. Thirty-two months after joining the study, 11 of the 43 'questionable dementia' patients met the criteria for probable AD diagnosis ('converters') and 29 remained free from AD ('non-converters'). Logistic regression analysis revealed that two tests of memory, in combination, could be used to predict a later diagnosis of probable AD with a high level of accuracy [¯2(3) = 47.054, p ! 0.0001]. As predicted, these tests are measures of visuospatial learning (CANTAB PAL) and, also, semantic memory (Graded Naming Test). These two tests in combination appear to be highly accurate in detecting cognitive dysfunction characteristic of preclinical AD. Using these tests, a simple algorithm is described for calculating, with 100% accuracy for this sample of 40 patients, the probability that an individual with mild memory impairments will go on to receive a diagnosis of probable AD.

Free recall and recognition are simulated in a network model of the hippocampal formation, incorporating simplified simulations of neurons, synaptic connections, and the effects of acetylcholine. Simulations focus on modeling the effects of the acetylcholine receptor blocker scopolamine on human memory. Systemic administration of scopolamine is modeled by blockade of the cellular effects of acetylcholine in the model, resulting in memory impairments replicating data from studies on human subjects. This blockade of cholinergic effects impairs the encoding of new input patterns (as measured by delayed free recall), but does not impair the delayed free recall of input patterns learned before the blockade. The impairment is selective to the free recall but not the recognition of items encoded under the influence of scopolamine. In the model, scopolamine blocks strengthening of recurrent connections in region CA3 to form attractor states for new items (encoding impaired) but allows recurrent excitation to drive the network into previously stored attractor states (retrieval spared). Neuron populations representing items (individual words) have weaker recurrent connections than neuron populations representing experimental context. When scopolamine further weakens the strength of recurrent connections it selectively prevents the subsequent reactivation of item attractor states by context input (impaired free recall) without impairing the subsequent reactivation of context attractor states by item input (spared recognition). This asymmetry in the strength of attractor states also allows simulation of the list-strength effect for free recall but not recognition. Simulation of a paired associate learning paradigm predicts that scopolamine should greatly enhance proactive interference due to retrieval of previously encoded associations during storage of new associations. © 1997 Elsevier Science B.V.

We tested the hypothesis that schizophrenia is primarily a frontostriatal disorder by examining executive function in first-episode patients. Previous studies have shown either equal decrements in many cognitive domains or specific deficits in memory. Such studies have grouped test results or have used few executive measures, thus, possibly losing information. We, therefore, measured a range of executive ability with tests known to be sensitive to frontal lobe function.

N-methyl-D-aspartate receptors (NMDARs) act as molecular coincidence detectors and allow for association or dissociation between preand postsynaptic neurons. NMDA receptors are central to remodeling of synaptic connections during postnatal development and associative learning abilities in adults. The ability to remodel neural networks is altered during postnatal development, possibly due to a change in the composition of NMDARs. That is, as forebrain systems (and cerebellum) develop, synaptic NR2B-containing NMDARs (NR2B-NMDARs) are replaced by NR2A-containing NMDARs (NR2A-NMDARs) and NR2B-NMDARs move to extrasynaptic sites. During the initial phase of the switch, synapses contain both NR2A-and NR2B-NMDARs and both long-term potentiation and long-term depression are enhanced. As NMDAR subunit expression decreases and NR2A-NMDARs come to predominate in the synapse, channel function and synaptic plasticity are reduced, and remodeling ability dissipates. The end result is a balance of plasticity and stability that is optimal for information processing and storage. Associative learning abilities involving different sensory modalities emerge sequentially, in accordance with synaptic maturation in related cortical and underlying brain structures. Thus, developmental alterations in NMDAR composition that occur at different ages in various brain structures may explain the protracted nature of the maturation of various associative learning abilities. #

Trace memories are formed when a stimulus event becomes associated with another event that occurs later in time and is discontinuous with the first event. The formation of trace memories enhances the survival of newly generated neurons in the dentate gyrus of the adult hippocampus (Gould et al., 1999a). Here we tested whether the acquisition of trace memories early during training is sufficient to enhance cell survival. We also examined whether the new neurons affected by trace memory formation persist indefinitely or only as long as the hippocampus is necessary for the expression of those memories. Groups of adult rats were injected with bromodeoxyuridine (BrdU), a marker of dividing cells, and trained 1 week later with paired stimuli using a trace eyeblink conditioning task or exposed to the same number of unpaired stimuli. Cell survival was assessed after different numbers of training trials and survival periods after training. Overall cell survival was not enhanced by exposure to 200 trials of paired stimuli during trace conditioning. However, there was a positive correlation between performance of individual animals and cell survival. In addition, exposure to 800 trials of paired stimuli during trace conditioning increased the number of BrdU-labeled cells 60 d after training. The vast majority of these cells were neurons and coexpressed the neuronal markers class III ␤-tubulin or neuronal nuclei. These data suggest that individual differences in associative learning predict whether new neurons will survive and that once affected, these neurons remain for months and beyond the time when they are required for the retention of trace memories.