Effects of pharmacologically induced changes in NMDA-receptor activity on long-term memory in humans

In a double-blind crossover design, either 30 mg of the noncompetitive NMDA-receptor antagonist memantine or a placebo was administered to 40 healthy male volunteers. Twenty line drawings of objects and 20 photographs of unfamiliar faces were presented on a computer screen. After a retention interval of 80 min, the participants' task was to select the original objects and faces from a set of 80 items. Results were analyzed applying a signal-detection-theory approach. Recognition performance for objects was significantly impaired under memantine as compared to placebo, whereas performance on face recognition was not affected. Findings support the notion of differential effects of NMDA-receptor antagonists on memory functions in humans.     

Working memory training: improving intelligence--changing brain activity

The main objectives of the study were: to investigate whether training on working memory (WM) could improve fluid intelligence, and to investigate the effects WM training had on neuroelectric (electroencephalography - EEG) and hemodynamic (near-infrared spectroscopy - NIRS) patterns of brain activity. In a parallel group experimental design, respondents of the working memory group after 30 h of training significantly increased performance on all tests of fluid intelligence. By contrast, respondents of the active control group (participating in a 30-h communication training course) showed no improvements in performance. The influence of WM training on patterns of neuroelectric brain activity was most pronounced in the theta and alpha bands. Theta and lower-1 alpha band synchronization was accompanied by increased lower-2 and upper alpha desynchronization. The hemodynamic patterns of brain activity after the training changed from higher right hemispheric activation to a balanced activity of both frontal areas. The neuroelectric as well as hemodynamic patterns of brain activity suggest that the training influenced WM maintenance functions as well as processes directed by the central executive. The changes in upper alpha band desynchronization could further indicate that processes related to long term memory were also influenced.     

Effects of green tea extract on learning, memory, behavior and acetylcholinesterase activity in young and old male rats

Objective

To study the effects of green tea extract administration on age-related cognition in young and old male Wistar rats.

Methods

Young and old rats were orally administered 0.5% green tea extract for a period of eight weeks and were evaluated by passive avoidance, elevated maze plus paradigm and changes in acetylcholinesterase activity.

Results

Treatment of young and old rats with the extract resulted in no significant difference in performance on the rota rod treadmill test/righting reflex time. Green tea extract significantly improved learning and memory in older rats, with increased retention latency to enter difference in passive avoidance test. In the elevated maze test, green tea treatment resulted in significantly more number of entries in the enclosed arm by the young and old rats. Decline in acetylcholinesterase activity was observed in the cerebrum of green tea treated old rats in comparison to the green tea treated young rats.

Conclusion

Green tea extract administration is effective in enhancing learning and memory in aged rats, and hence, may serve useful in reversing age-related deficits.     

Mismaking memories: neural precursors of memory illusions in electrical brain activity

Memory illusions--vivid experiences of events that never occurred--could result from inaccuracies either in retrieving memories or in initially storing them. In two experiments, people studied lists of associated words that either did or did not induce later illusory (false) memories of associated but nonpresented lure words. The amplitude of the electrical brain activity during study of words (approximately 500-1,300 ms) that were themselves later correctly remembered reliably distinguished list words that led to such illusory memories from those that did not. This encoding difference associated with subsequent illusory memory (referred to as a DIM)--presumably reflecting item-specific encoding differences--is a neural precursor of memory illusions.     

Order information in working memory: an integrative review of evidence from brain and behavior

Evidence about memory for order information comes from a number of different methodologies: human cognition, patient studies, neuroimaging studies, and animal lesion and behavioral studies. The present article discusses (a) evidence that order and item memory are separable; (b) proposed mechanisms for order memory (interitem associations, direct codes, hierarchical codes, feature codes, and magnitude codes) and evidence for each; (c) evidence for the neural substrates of order memory from patient, neuroimaging, and animal lesion and single-cell recording studies; (d) barriers to integration between the disciplines; and (e) suggestions for better coordination of efforts between the different disciplines.     

Effects of memory aids on hypothesis behavior and focusing in young children and adults

In Experiment 1, five groups of second graders were administered a series of blank-trials problems under the following testing conditions: (a) with standard procedures, (b) with a reduced set of potentially correct hypotheses (Hs), (c) with a memory aid, (d) with memory plus recoding aids, and (e) with memory and recoding aids in addition to having the Ss' attention closely directed to the potentially positive Hs. In Experiment 2, four groups of college students were given a similar series of blank-trials problems only now with 16 rather than 8 potentially correct Hs. The condition corresponding to (b) was omitted.In both experiments, all groups reliably used H-defining response sequences on the blank trials. In addition, the focusing functions for all groups receiving training aids closely approximated an ideal focusing function and were reliably different from the functions for the groups trained under standard conditions. The improvements in focusing were closely matched by higher levels of performance on the component process of coding, recording, and retention of remote outcome information, lending support to the assumption that a complex process such as focusing can be analyzed into measurable components. It was further concluded that deficiencies in focusing may well be a function of the unavailability of the relevant information rather than to an absence of the necessary rules, as has often been assumed with young children.     

Alterations in error-related brain activity and post-error behavior over time

This study examines the relation between the error-related negativity (ERN) and post-error behavior over time in healthy young adults (N=61). Event-related brain potentials were collected during two sessions of an identical flanker task. Results indicated changes in ERN and post-error accuracy were related across task sessions, with more negative ERN associated with greater improvements in post-error accuracy. This relationship was independent of any cross-sectional relationships between overall task performance, individual difference factors, including personality and self-efficacy, and indices of self-regulatory action monitoring. These results indicate that the relation between ERN and post-error accuracy remains intact and consistent regardless of variation in this set of individual difference factors previously associated with both of these indices of self-regulatory action monitoring, providing support for the strength, robustness, and persistence of this relationship in the process of adaptively controlling behavior to enhance task performance.     

The readiness potential--movement-correlated changes in bioelectric brain activity

The Bereitschaftspotential which belongs to the group of slow potentials can be recorded in the period of preparation to a voluntary motor act and is connected with changes of the level of central nervous activation. This paper is concerned with general questions of classification of Bp in the complex of movement-related brain potentials, with the topographic distribution over the scalp, and with the relation of Bp to some motor functions of the cortex. The relationship to psychological factors affecting the Bp is discussed.     

Unraveling mechanisms for expert object recognition: bridging brain activity and behavior

Behavioral sensitivity to object transformations and the response to novel objects (Greebles) in the fusiform face area (FFA) was measured several times during expertise training. Sensitivity to 3 transformations increased with expertise: (a) configural changes in which halves of objects were misaligned, (b) configural changes in which some of the object parts were moved, and (c) the substitution of an object part with a part from a different object. The authors found that holistic-configural effects can arise from object representations that are differentiated in terms of features or parts. Moreover, a holistic-inclusive effect was correlated with changes in the right FFA. Face recognition may not be unique in its reliance on holistic processing, measured in terms of both behavior and brain activation.     

Effects of availability of feature changes on behavior segmentation

Thirty-five subjects segmented one of two videotapes of an actor methodically assembling 20 five-page questionnaires. In one sequence, the completion of each questionnaire resulted in a highly visible change in the stimulus fields: The top page of the stack changed from black to white or from white to black with the completion of each questionnaire. In a second sequence the action was identical, but the changing feature was concealed from view. Results disclosed that subjects viewing the tape with the visible change segmented the action on the basis of that change. Subjects viewing the same action without the visible change segmented the behavior into its fine-unit components, despite the fact that the higher-level organization in the behavior was readily understood.     

Organization in memory and behavior

Some common reinforcement contingencies make the delivery of a reinforcer depend on the occurrence of behavior lacking significant temporal structure: a reinforcer may be contingent on nearly instantaneous responses such as a pigeon's key peck, a rat's lever press, a human's button press or brief verbal utterance, and so on. Such a reinforcement contingency conforms much more closely to the functionalist tradition in experimental psychology than to the structuralist tradition. Until recently, the functionalist tradition, in the form of a kind of associationism, typified most research on human learning and memory. Recently, however, research on human memory has focused more on structural issues: now the basic unit of analysis often involves an organized temporal pattern of behavior. A focus on the interrelations between the function and structure of behavior identifies a set of independent and dependent variables different from those identified by certain common kinds of “molar” behavioral analyses. In so doing, such a focus redefines some of the significant issues in the experimental analysis of behavior.     

Age-related changes in working and reference memory performance and locomotor activity in the Wistar rat

Wistar rats of three age groups were tested in an automated tunnel-maze system of variable geometry to investigate whether changes in spontaneous locomotor activity and in learning and memory develop differentially or in a correlated fashion as a function of age. Senescent (30 months) as well as mature-adult (17 months) rats showed an age-correlated decline of locomotor activity as compared to the mature-young (5 months) group. Both working-memory (measured as within-trial arm discrimination performance) and reference-memory (measured as avoidance of "blind alley" visits) were severely affected in the senescent group, whereas the middle-aged animals suffered only from a working-memory deficit. The findings provide evidence that locomotor deficits do not necessarily interfere in the assessment of age-related changes in cognitive performance. Furthermore the results support the hypothesis that working and reference memory have different underlying physiological correlates and that these neuronal systems are differentially affected by the aging process.     

Visual and tactile memory for 2-D patterns: Effects of changes in size and left-right orientation

Visual identification of 3-D objects depends on representations that are invariant across changes in size and left-right orientation. We examined whether this finding reflects the unique demands of processing 3-D objects, or whether it generalizes to 2-D patterns and to the tactile modality. Our findings suggest that object representation for identification is influenced greatly by the processing demands of stimulus materials (e.g., 2-D vs. 3-D objects) and stimulus modality (touch vs. vision). Identification of 2-D patterns in vision is adversely affected by left-right orientation changes, but not size changes. Identification of the same patterns in touch is adversely affected by both changes. Together, the results suggest that the unique processing demands of stimulus materials and modality shape the representation of objects in memory.     

Trait memory and behavior memory: the effects of alternative pathways on impression judgment response times

Carlston (1980a) and Lingle (1983) argued that remembered behaviors, previous trait inferences, or both may be accessed and used in making new trait inferences, depending on a variety of factors. In this article we relate this argument to a spreading activation model of memory and suggest factors that should affect the relative accessibility of inferences and behaviors during trait judgment processes. In our study we varied several of these factors and assessed accessibility, using response-time methods. The results of this study strongly support the model's prediction that prompting inference formation facilitates subsequent trait judgment response times, but only when relevant behavior memories have not been recently primed. We theorize that the inference manipulations used in this study strengthened the direct pathway to a relevant trait concept, but that the strength of this pathway was immaterial to judgment response times when a "proximal prime" directed retrieval efforts along an alternative "behavioral" route to the trait information. The results also suggest that the proximal behavior prime facilitated trait responses among subjects who had not been induced to make trait inferences, but slowed trait responses among subjects who had previously been induced to make trait inferences.     

Effects of feedback reliability on feedback-related brain activity: A feedback valuation account

Adaptive decision making relies on learning from feedback. Because feedback sometimes can be misleading, optimal learning requires that knowledge about the feedback’s reliability be utilized to adjust feedback processing. Although previous research has shown that feedback reliability indeed influences feedback processing, the underlying mechanisms through which this is accomplished remain unclear. Here we propose that feedback processing is adjusted by the adaptive, top-down valuation of feedback. We assume that unreliable feedback is devalued relative to reliable feedback, thus reducing the reward prediction errors that underlie feedback-related brain activity and learning. A crucial prediction of this account is that the effects of feedback reliability are susceptible to contrast effects. That is, the effects of feedback reliability should be enhanced when both reliable and unreliable feedback are experienced within the same context, as compared to when only one level of feedback reliability is experienced. To evaluate this prediction, we measured the event-related potentials elicited by feedback in two experiments in which feedback reliability was varied either within or between blocks. We found that the fronto-central valence effect, a correlate of reward prediction errors during reinforcement learning, was reduced for unreliable feedback. But this result was obtained only when feedback reliability was varied within blocks, thus indicating a contrast effect. This suggests that the adaptive valuation of feedback is one mechanism underlying the effects of feedback reliability on feedback processing.     

Effects of peripheral immune activation on social behavior and adrenocortical activity in aggressive mice: Genotype-environment interactions

To explore genetic-developmental differences in the biobehavioral effects of induced illness, males from two lines of mice selectively bred for high or low levels of aggressive behavior were injected with endotoxin (Escherichia coli, LPS: 0.25 mg/kg, 1.25 mg/kg, or 2.5 mg, i.p.) or saline. Body temperature, weight, and locomotor activity were monitored immediately before and 8 and 24 hr after injection. Twenty-four hours after injection, social behaviors were assessed in a 10-min dyadic test, and hypothalamus, spleen, and serum were collected. In both lines, endotoxin treatment increased behavioral immobility ("freezing") and decreased social exploration. Other effects showed line differences: Males from the high-aggressive line had a lower threshold to endotoxin-induced effects on body temperature, weight loss, spleen weight, and corticosterone. Social reactivity (startle response to mild social investigation) increased in the high-aggressive line and decreased in the low-aggressive line after treatment. In the high-aggressive line only, endotoxin decreased attack frequency and increased latency to attack. The interactions between selected line (genotype) and endotoxin treatment (environment) demonstrate that genetic-developmental differences in social and aggressive behavior may indicate the extent to which immune stimuli (e.g., bacteria, viruses, cytokines) function as "biobehavioral stressors." Aggr. Behav. 23:93–105, 1997.© 1997 Wiley-Liss, Inc.     

Context preexposure prevents forgetting of a contextual fear memory: implication for regional changes in brain activation patterns associated with recent and remote memory tests

Contextual fear conditioning was maintained over a 15-day retention interval suggesting no forgetting of the conditioning experience. However, a more subtle generalization test revealed that, as the retention interval increased, rats showed enhanced generalized fear to an altered context. Preexposure to the training context prior to conditioning, however, prevented this enhanced generalized fear from developing. These results support the hypothesis that the memory representation of the context degrades as the memory ages and is responsible for enhanced generalization. The implications of these results for systems consolidation versus forgetting interpretations of regional changes in neural activation patterns that occur as memories age are discussed.