Repetition suppression and multi-voxel pattern similarity differentially track implicit and explicit visual memory.

Repeated exposure to a visual stimulus is associated with corresponding reductions in neural activity, particularly within visual cortical areas. It has been argued that this phenomenon of repetition suppression is related to increases in processing fluency or implicit memory. However, repetition of a visual stimulus can also be considered in terms of the similarity of the pattern of neural activity elicited at each exposure--a measure that has recently been linked to explicit memory. Despite the popularity of each of these measures, direct comparisons between the two have been limited, and the extent to which they differentially (or similarly) relate to behavioral measures of memory has not been clearly established. In the present study, we compared repetition suppression and pattern similarity as predictors of both implicit and explicit memory. Using functional magnetic resonance imaging, we scanned 20 participants while they viewed and categorized repeated presentations of scenes. Repetition priming (facilitated categorization across repetitions) was used as a measure of implicit memory, and subsequent scene recognition was used as a measure of explicit memory. We found that repetition priming was predicted by repetition suppression in prefrontal, parietal, and occipitotemporal regions; however, repetition priming was not predicted by pattern similarity. In contrast, subsequent explicit memory was predicted by pattern similarity (across repetitions) in some of the same occipitotemporal regions that exhibited a relationship between priming and repetition suppression; however, explicit memory was not related to repetition suppression. This striking double dissociation indicates that repetition suppression and pattern similarity differentially track implicit and explicit learning.

Poorer aerobic fitness relates to reduced integrity of multiple memory systems.

Epidemiological investigations have revealed increases in the prevalence of sedentary behaviors in industrialized societies. However, the implications of those lifestyle choices and related cardiorespiratory fitness levels for memory function are not well-understood. To determine the extent to which cardiorespiratory fitness relates to the integrity of multiple memory systems, a cross-sectional sample of young adults were tested over the course of 3 days in areas related to implicit memory, working memory, long-term memory, and aerobic fitness. Findings revealed an association between aerobic fitness and memory function such that individuals with lower cardiorespiratory fitness exhibited poorer implicit memory performance and poorer long-term memory retention. These data indicate that cardiorespiratory fitness may be important for the optimal function of neural networks underlying these memory systems.

Niche-specific cognitive strategies: object memory interferes with spatial memory in the predatory bat Myotis nattereri.

Related species with different diets are predicted to rely on different cognitive strategies: those best suited for locating available and appropriate foods. Here we tested two predictions of the niche-specific cognitive strategies hypothesis in bats, which suggests that predatory species should rely more on object memory than on spatial memory for finding food and that the opposite is true of frugivorous and nectivorous species. Specifically, we predicted that: (1) predatory bats would readily learn to associate shapes with palatable prey and (2) once bats had made such associations, these would interfere with their subsequent learning of a spatial memory task. We trained free-flying Myotis nattereri to approach palatable and unpalatable insect prey suspended below polystyrene objects. Experimentally naïve bats learned to associate different objects with palatable and unpalatable prey but performed no better than chance in a subsequent spatial memory experiment. Because experimental sequence was predicted to be of consequence, we introduced a second group of bats first to the spatial memory experiment. These bats learned to associate prey position with palatability. Control trials indicated that bats made their decisions based on information acquired through echolocation. Previous studies have shown that bat species that eat mainly nectar and fruit rely heavily on spatial memory, reflecting the relative consistency of distribution of fruit and nectar compared with insects. Our results support the niche-specific cognitive strategies hypothesis and suggest that for gleaning and clutter-resistant aerial hawking bats, learning to associate shape with food interferes with subsequent spatial memory learning.

Stress modulates the engagement of multiple memory systems in classification learning.

Learning and memory are supported by anatomically and functionally distinct systems. Recent research suggests that stress may alter the contributions of multiple memory systems to learning, yet the underlying mechanism in the human brain remains completely unknown. Using event-related functional magnetic resonance imaging, we asked in the present experiment whether stress may modulate the engagement of hippocampus-based "declarative" and striatum-based "procedural" memory systems during classification learning in humans and what brain mechanisms are involved in this effect. We found that stress reduced declarative knowledge about the learning task and changed the used learning strategy from a single-cue-based declarative strategy to a multicue-based procedural strategy, whereas learning performance per se remained unaffected by stress. Neuroimaging revealed that hippocampal activity correlated positively with task performance in the control condition, whereas striatal activity correlated with performance in the stress condition. After stress, hippocampal activity was reduced and even negatively correlated with learning performance. These findings show for the first time that stress alters the engagement of multiple memory systems in the human brain. Stress impaired the hippocampus-dependent system and allowed the striatum to control behavior. The shift toward "procedural" learning after stress appears to rescue task performance, whereas attempts to engage the "declarative" system disrupt performance.

Ranking of dental and somatic pain sensations among paediatric dental patients.

BACKGROUND: Children suffer from somatic and dental pain, which may interfere with their everyday life. Pain self-report tools are available for children. Research is needed to better understand the perception of dental pain in comparison with pain in other organs. AIM: To investigate relations between the perceptions of dental and somatic pain complaints among school-age children. DESIGN: One hundred and two children, aged 7-17 years (mean age, 11.5 ± 2.65 years), completed questioners regarding their somatic and dental: 1. Memory pain rank (MPR) and 2. Wong-Baker FACES Pain Rating Scale (FRS). RESULTS: Children reported increased dental pain after school in both scales (P = 0.015 in MPR). In both MPR and FRS, the pattern of pain ranking was similar: Abdominal pain was scored highest (2.75 ± 1.4 and 1.56 ± 1.63, respectively), followed by headache, ear, dental and TMJ (Temporomandibular joint). CONCLUSION: There was a strong correlation between pain perception and current pain scores in every organ. Somatic pain, namely head, abdomen and ears, was ranked significantly higher than dental and TMJ pain. School-aged children rank current pain and pain experience significantly lower while they are pre-occupied (school time) in comparison with times when they are less busy (after school time).

Neuropsychological assessment of memory in preschoolers.

Memory is of fundamental importance for cognitive, social, and educational function, making it a target for neuropsychological assessment. The subject of this review is one particular type of memory, namely, episodic memory of unique events and experiences. Episodic memory allows for rapid, even one-trial learning of new information and retention of it for later retrieval. It depends on a particular neural substrate that undergoes a protracted developmental course. The review features discussion of some of the challenges associated with valid assessment of this specific form of memory in the preschool period, as well as a description and critical evaluation of available standardized measures. It also features description of two new approaches to assessment of episodic memory and their sensitivity to memory-specific deficits in the preschool years and in infancy. The review ends with introduction of the NIH Toolbox Picture Sequence Memory Test, designed as a measure of episodic memory in the preschool years and beyond.

Time scales of memory, learning, and plasticity.

After only about 10 days would the storage capacity of our nervous system be reached if we stored every bit of input. The nervous system relies on at least two mechanisms that counteract this capacity limit: compression and forgetting. But the latter mechanism needs to know how long an entity should be stored: some memories are relevant only for the next few minutes, some are important even after the passage of several years. Psychology and physiology have found and described many different memory mechanisms, and these mechanisms indeed use different time scales. In this prospect we review these mechanisms with respect to their time scale and propose relations between mechanisms in learning and memory and their underlying physiological basis.

"Identify-to-reject": a specific strategy to avoid false memories in the DRM paradigm.

Previous research using the Deese-Roediger-McDermott (DRM) paradigm has shown that lists of associates in which the critical words were easily identified as the themes of the lists produce lower levels of false memories in adults. In an attempt to analyze whether this effect is due to the application of a specific memory-editing process (the identify-to-reject strategy), two experiments manipulated variables that are likely to disrupt this strategy either at encoding or at retrieval. In Experiment 1, lists were presented at a very fast presentation rate to reduce the possibility of identifying the missing critical word as the theme of the list, and in Experiment 2, participants were pressed to give yes/no recognition answers within a very short time. The results showed that both of these manipulations disrupted the identifiability effect, indicating that the identify-to-reject strategy and theme identifiability play a major role in the rejection of false memories in the DRM paradigm.

Type or dimension? A taxometric investigation of flashbulb memories.

Flashbulb memories (FBMs) have been defined as vivid and detailed memory of a reception context under which one first heard of a public and unexpected emotional event. One of the issues still open for research on FBMs is to understand whether this latent construct has to be conceptualised as a continuum with other autobiographical memories, or whether it represents a special cluster of memories. This theoretical distinction has some implications for the measurement of the phenomenon, that could be assessed by a dimensional or categorical (taxonic) model. The current study attempted to provide an empirical answer to the problem of FBM measurement, by adopting a taxometric analysis. The main strength of these analyses is to treat taxonic and dimensional models as two competing hypotheses and to evaluate the relative support for each of them. Taxometric analyses were applied to FBM data for the Pope's death, and results supported the taxonic structure of FBMs.

PKA and PKC are required for long-term but not short-term in vivo operant memory in Aplysia.

We investigated the involvement of PKA and PKC signaling in a negatively reinforced operant learning paradigm in Aplysia, learning that food is inedible (LFI). In vivo injection of PKA or PKC inhibitors blocked long-term LFI memory formation. Moreover, a persistent phase of PKA activity, although not PKC activity, was necessary for long-term memory. Surprisingly, neither PKA nor PKC activity was required for associative short-term LFI memory. Additionally, PKA and PKC were not required for the retrieval of short- or long-term memory (STM and LTM, respectively). These studies have identified key differences between the mechanisms underlying nonassociative sensitization, operant reward learning, and LFI memory in Aplysia.

Construction of a memory battery for computerized administration, using item response theory.

In accordance with Item Response Theory, a computer memory battery with six tests was constructed for use in the Portuguese adult population. A factor analysis was conducted to assess the internal structure of the tests (N = 547 undergraduate students). According to the literature, several confirmatory factor models were evaluated. Results showed better fit of a model with two independent latent variables corresponding to verbal and non-verbal factors, reproducing the initial battery organization. Internal consistency reliability for the six tests were alpha = .72 to .89. IRT analyses (Rasch and partial credit models) yielded good Infit and Outfit measures and high precision for parameter estimation. The potential utility of these memory tasks for psychological research and practice willbe discussed.

Memory dysfunction in panic disorder: an investigation of the role of chronic benzodiazepine use.

BACKGROUND: Studies of the neurocognitive effects of long-term benzodiazepine use have been confounded by the presence of neurocognitive deficits characterizing the clinical conditions for which these medications are taken. Similarly, studies of the neurocognitive effects of anxiety disorders have been confounded by the inclusion of chronically benzodiazepine-medicated patients. This study was designed to tease apart the potentially confounding effects of long-term benzodiazepine use and panic disorder (PD) on memory and visuoconstructive abilities. METHODS: Twenty chronically benzodiazepine-medicated and 20 benzodiazepine-free patients with PD with agoraphobia were compared with a group of 20 normal control participants, group-matched for age, education, and gender on a battery of neuropsychological tests assessing short-term, episodic long-term, and semantic memory, as well as visuoconstructive abilities. RESULTS: Results indicated that benzodiazepine-free panic patients were relatively impaired in nonverbal short-term and nonverbal episodic long-term memory and visuoconstructive abilities, whereas verbal short-term and verbal episodic memory and semantic memory were preserved. Only limited evidence was found for more pronounced impairments in chronically benzodiazepine-medicated PD patients. CONCLUSIONS: This study provides evidence that patients with PD are characterized by relative impairments in nonverbal memory and visuoconstructive abilities, independent of benzodiazepine use. Nonetheless, we found evidence that chronic treatment with benzodiazepines is associated with intensification of select relative impairments in this realm. Documentation of these deficits raises questions about the broader etiology of neurocognitive impairment in PD as well as its impact on daily functioning.

Predictive, interactive multiple memory systems.

Most lesion studies in animals, and neuropsychological and functional neuroimaging studies in humans, have focused on finding dissociations between the functions of different brain regions, for example in relation to different types of memory. While some of these dissociations can be questioned, particularly in the case of neuroimaging data, we start by assuming a "modal model" in which at least three different memory systems are distinguished: an episodic system (which stores associations between items and spatial/temporal contexts, and which is supported primarily by the hippocampus); a semantic system (which extracts combinations of perceptual features that define items, and which is supported primarily by anterior temporal cortex); and modality-specific perceptual systems (which represent the sensory features extracted from a stimulus, and which are supported by higher sensory cortices). In most situations however, behavior is determined by interactions between these systems. These interactions reflect the flow of information in both "forward" and "backward" directions between memory systems, where backward connections transmit predictions about the current item/features based on the current context/item. Importantly, it is the resulting "prediction error"--the difference between these predictions and the forward transmission of sensory evidence--that drives memory encoding and retrieval. We describe how this "predictive interactive multiple memory systems" (PIMMS) framework can be applied to human neuroimaging data acquired during encoding or retrieval phases of the recognition memory paradigm. Our novel emphasis is thus on associations rather than dissociations between activity measured in key brain regions; in particular, we propose that measuring the functional coupling between brain regions will help understand how these memory systems interact to guide behavior.

Olfactory performance in AD, aMCI, and healthy ageing: a unirhinal approach.

Olfactory dysfunction constitutes one of the earliest signs of Alzheimer's disease (AD) and has been shown in individuals with amnestic mild cognitive impairment (aMCI). Whether the severity of olfactory impairments in aMCI patients parallels those in AD has not been clearly established. In addition, given reports of asymmetries in neuropathological burden in early AD, functional asymmetries in olfactory performance may enhance early detection if olfactory function is assessed unirhinally. We compared AD, aMCI, and healthy participants on olfactory identification and memory assessed unirhinally. Olfactory identification was most proficient in the healthy participants and least proficient in AD, although this disparity did not depend on nostril side. Nevertheless, when only the worst nostril of each participant was included in the analysis, aMCI patients outperformed their AD counterparts. In contrast, when only the best nostril of each participant was included in the analysis--often regarded as an estimate of birhinal performance--this difference between aMCI and AD dissipated. Olfactory memory did not differ significantly across the groups, perhaps reflecting a floor effect. The findings support the hypothesis that unirhinal olfactory assessment may assist in differentiating between demented and nondemented individuals.

Different spatial memory systems are involved in small- and large-scale environments: evidence from patients with temporal lobe epilepsy.

Recent reports show that humans and animals do not acquire information about routes and object locations in the same way. In spatial memory, a specific sub-system is hypothesized to be involved in encoding, storing and recalling navigational information, and it is segregated from the sub-system devoted to small-scale environment. We assessed this hypothesis in a sample of patients treated surgically for intractable temporal lobe epilepsy. We found double dissociations between learning and recall of spatial positions in large space versus small space. These results strongly support the hypothesis that two segregate systems process navigational memory for large-scale environments and spatial memory in small-scale environments.

Differential contributions of objective memory and mood to subjective memory complaints in refractory focal epilepsy.

People with epilepsy frequently present with bitter memory complaints. Previous research variously attributes this to symptoms of mood disturbance or objective memory deficits. To investigate the influence of the epileptogenic region on this variability, we examined interrelationships between mood, objective memory, and memory complaints in a sample of patients with refractory focal epilepsy and controls (N = 96). Patients had either mesial temporal (MT, n = 39) or non mesial-temporal (NMT, n = 21) foci. In contrast to controls (n = 36), both patient groups were highly concerned about their memory (P<0.001) and were more likely to have a history of depression (P = 0.005). Multiple regression showed that objective memory dysfunction and current depressive symptoms predicted the memory complaints of patients with MT epilepsy (P = 0.005), whereas a history of depression predicted the complaints of patients with NMT epilepsy (P = 0.008). These findings suggest that patients have concerns about their memory underpinned by distinct psychological and neurobiological factors depending on the location of their epileptogenic focus.

A histogram based method for multiclass classification using SVMs.

SVMs were primarily proposed to deal with binary classification. In this work an alternative O(log(2)(n)) method for multiple classes classification using SVMs is proposed. Experimental results showed that it can be 23 times faster than the one vs one method, and 1.3 times faster than the one vs all classic methods, with the same error rate. Tests were performed on a speaker independent, isolated word speech recognition scenario.

A Common Task Structure Links Together the Fate of Different Types of Memories.

Our memories frequently have features in common. For example, a learned sequence of words or actions can follow a common rule, which determines their serial order, despite being composed of very different events [1, 2]. This common abstract structure might link the fates of memories together. We tested this idea by creating different types of memory task: a sequence of words or actions that either did or did not have a common structure. Participants learned one of these memory tasks and then they learned another type of memory task 6 h later, either with or without the same structure. We then tested the newly formed memory's susceptibility to interference. We found that the newly formed memory was protected from interference when it shared a common structure with the earlier memory. Specifically, learning a sequence of words protected a subsequent sequence of actions learned hours later from interference, and conversely, learning a sequence of actions protected a subsequent sequence of words learned hours later from interference provided the sequences shared a common structure. Yet this protection of the newly formed memory came at a cost. The earlier memory had disrupted recall when it had the same rather than a different structure to the newly formed and protected memory. Thus, a common structure can determine what is retained (i.e., protected) and what is modified (i.e., disrupted). Our work reveals that a shared common structure links the fate of otherwise different types of memories together and identifies a novel mechanism for memory modification.

An historical perspective on Endel Tulving's episodic-semantic distinction.

The distinction between episodic and semantic memory, proposed by Endel Tulving in 1972, remains a key concept in contemporary Cognitive Neuroscience. Here we review how this distinction evolved in Tulving's writings over the years. Crucially, from 1972 onward, he argued that the two forms of memory were inter-dependent and that their interaction was an essential feature of normal episodic memory function. Moreover, later elaborations of the theory clearly proposed that these interactions formed the basis of normal declarative memory functioning. A later but crucial aspect of Tulving's contribution was his stress on the importance of subjective experience, which, according to him, "should be the ultimate object of interest, the central aspect of remembering that is to be explained and understood". We relate these and his numerous other ideas to current perspectives about the organization and function of human memory.