The neurobiology of semantic memory

Semantic memory includes all acquired knowledge about the world and is the basis for nearly all human activity, yet its neurobiological foundation is only now becoming clear. Recent neuroimaging studies demonstrate two striking results: the participation of modality-specific sensory, motor, and emotion systems in language comprehension, and the existence of large brain regions that participate in comprehension tasks but are not modality-specific. These latter regions, which include the inferior parietal lobe and much of the temporal lobe, lie at convergences of multiple perceptual processing streams. These convergences enable increasingly abstract, supramodal representations of perceptual experience that support a variety of conceptual functions including object recognition, social cognition, language, and the remarkable human capacity to remember the past and imagine the future.     

The neurobiology of human category learning

Categorization is among the most important skills that any organism can possess. Recent advances in cognitive neuroscience have led to new insights about the neural basis of category learning. Perhaps most important is the finding that many different, widely separated neural structures appear to participate in category learning, but to varying degrees that depend on category structure. In particular, different brain regions are implicated according to whether the category-learning task involves explicit rules, prototype distortion or information integration.     

The neurobiology of fear memory reconsolidation and psychoanalytic theory

Advances in both experimental neuroscience and psychoanalytic theory and technique have made it possible to consider mechanisms by which psychodynamic psychotherapies might have an impact at the cellular and molecular level. Here potential analogies are drawn between (1) the mechanisms and results of blocking the reconsolidation of conditioned fear memories in the laboratory and (2) several key aspects of psychoanalytic process. A review of the biology of conditioned fear memory, including differences between extinction and inhibition of reconsolidation, indicates that this biology may have relevance to various ways in which psychoanalytic therapy is effective. The ideas proposed here might lead to further experimental attempts to understand the molecular biology of psychoanalysis.     

The novel object recognition memory: neurobiology, test procedure, and its modifications

Animal models of memory have been considered as the subject of many scientific publications at least since the beginning of the twentieth century. In humans, memory is often accessed through spoken or written language, while in animals, cognitive functions must be accessed through different kind of behaviors in many specific, experimental models of memory and learning. Among them, the novel object recognition test can be evaluated by the differences in the exploration time of novel and familiar objects. Its application is not limited to a field of research and enables that various issues can be studied, such as the memory and learning, the preference for novelty, the influence of different brain regions in the process of recognition, and even the study of different drugs and their effects. This paper describes the novel object recognition paradigms in animals, as a valuable measure of cognition. The purpose of this work was to review the neurobiology and methodological modifications of the test commonly used in behavioral pharmacology.     

Animal learning and memory and their relation to human learning and memory

For some three decades now, the experimental study of learning and memory has been conducted as two entirely separate endeavors, one using humans as subjects and the other using animals. The separation is placed in historical context, and consideration is given to recent movements by those in the animal camp toward adopting some of the theorizing as well as some of the list memory procedures from those in the human camp. It is argued that exploring list memory in animals should do much to further our understanding of both animal cognition and its relation to human cognition. The trend toward more complex theorizing and more liberal use of hypothetical constructs, on the other hand, is regarded with concern. It is argued that hypothetical constructs have contributed little to an enduring understanding of human learning and memory, and that they are unlikely to be any more helpful with animals.     

The relation between recognition memory and classification learning

Two experiments investigated the relation between recognition memory and classification learning. The subjects were instructed that they would see a series of random-dot patterns and later would be asked to classify or to recognize the patterns. Following study, the subjects performed a classification task, a recognition-memory task, or both. It was found that classification-learning instructions were superior to recognition-memory instructions for the classification task, but that there was little or no effect of instructions on the recognition task. When subjects performed both recognition and classification tasks, there was no relation between saying “old” to a probe and correctly classifying it, except with old exemplars, and then only when the initial instructions had been to expect a recognition-memory test. Overall, the data show that classification and recognition can be experimentally separated. In addition, classification is often statistically independent of recognizing that items are old. These observed relations provide some constraints for the further development of models of classification learning and recognition memory.     

The neurobiology of adaptive learning in reading: A contrast of different training conditions

fMRI was used to investigate the separate influences of orthographic, phonological, and semantic processing on the ability to learn new words and the cortical circuitry recruited to subsequently read those words. In a behavioral session, subjects acquired familiarity for three sets of pseudowords, attending to orthographic, phonological, or (learned) semantic features. Transfer effects were measured in an event-related fMRI session as the subjects named trained pseudowords, untrained pseudowords, and real words. Behaviorally, phonological and semantic training resulted in better learning than did orthographic training. Neurobiologically, orthographic training did not modulate activation in the main reading regions. Phonological and semantic training yielded equivalent behavioral facilitation but distinct functional activation patterns, suggesting that the learning resulting from these two training conditions was driven by different underlying processes. The findings indicate that the putative ventral visual word form area is sensitive to the phonological structure of words, with phonologically analytic processing contributing to the specialization of this region.     

What artificial grammar learning reveals about the neurobiology of syntax

In this paper we examine the neurobiological correlates of syntax, the processing of structured sequences, by comparing FMRI results on artificial and natural language syntax. We discuss these and similar findings in the context of formal language and computability theory. We used a simple right-linear unification grammar in an implicit artificial grammar learning paradigm in 32 healthy Dutch university students (natural language FMRI data were already acquired for these participants). We predicted that artificial syntax processing would engage the left inferior frontal region (BA 44/45) and that this activation would overlap with syntax-related variability observed in the natural language experiment. The main findings of this study show that the left inferior frontal region centered on BA 44/45 is active during artificial syntax processing of well-formed (grammatical) sequence independent of local subsequence familiarity. The same region is engaged to a greater extent when a syntactic violation is present and structural unification becomes difficult or impossible. The effects related to artificial syntax in the left inferior frontal region (BA 44/45) were essentially identical when we masked these with activity related to natural syntax in the same subjects. Finally, the medial temporal lobe was deactivated during this operation, consistent with the view that implicit processing does not rely on declarative memory mechanisms that engage the medial temporal lobe. In the context of recent FMRI findings, we raise the question whether Broca’s region (or subregions) is specifically related to syntactic movement operations or the processing of hierarchically nested non-adjacent dependencies in the discussion section. We conclude that this is not the case. Instead, we argue that the left inferior frontal region is a generic on-line sequence processor that unifies information from various sources in an incremental and recursive manner, independent of whether there are any processing requirements related to syntactic movement or hierarchically nested structures. In addition, we argue that the Chomsky hierarchy is not directly relevant for neurobiological systems.     

The role of working memory in motor learning and performance

Three experiments explore the role of working memory in motor skill acquisition and performance. Traditional theories postulate that skill acquisition proceeds through stages of knowing, which are initially declarative but later procedural. The reported experiments challenge that view and support an independent, parallel processing model, which predicts that procedural and declarative knowledge can be acquired separately and that the former does not depend on the availability of working memory, whereas, the latter does. The behaviour of these two processes was manipulated by providing or withholding visual (and auditory) appraisal of outcome feedback. Withholding feedback was predicted to inhibit the use of working memory to appraise success and, thus, prevent the formation of declarative knowledge without affecting the accumulation of procedural knowledge. While the first experiment failed to support these predictions, the second and third experiments demonstrated that procedural and declarative knowledge can be acquired independently. It is suggested that the availability of working memory is crucial to motor performance only when the learner has come to rely on its use.     

The neurobiology of postpartum depression

Postpartum psychiatric changes can range from maternity blues to psychosis. Causality is still undetermined, but explanations for these disturbances often focus on hormonal changes and dysregulation. Researchers have begun the process of delineating what neurobiological factors may be associated with depressive disorders in pregnancy and the postpartum. This article reviews the current literature on the roles of gonadal and pituitary hormones in the psychopathophysiology of postpartum mood disorders. Other biological factors, such as biogenic amines, neuroactive steroids, cholesterol, and fatty acids, are also discussed. The potential benefits of neuroimaging to aid in understanding neuropsychiatric changes that occur in the context of postpartum depression are also considered.     

The neurobiology of abandonment homicide

A review is made of the typical modus operandi and psychological profile of uxoricide (wife murder) perpetrators. Typically, most had traumatic childhood and have current personality disorders (PD; typically Dependent, Passive–Aggressive, or Borderline PD). The uxoricide occurred during attempted abandonment of the relationship by the female and was characterized by extreme violence and elements of disorganized behavior by the perpetrator. A review is also made of the neuroanatomy and neurobiology of aggression. It is found that the orbitofrontal cortex (OFC) is implicated in control of aggressive impulses. This cortical area matures during the critical “rapprochement subphase” of early development (1.5–2 years). Attachment dysfunction during this period may interfere with critical development. It is found that low levels of serotonin (5-HT) and high levels of norepinephrine (NE) are implicated in aggression. It is also found that low levels of 5-HT and high levels of NE are long-term neurobiological sequelae of trauma. Attachment trauma can occur during the rapprochement subphase. It is suggested that a biological basis may serve to connect early trauma experience with a specific rage response to abandonment and spousal homicide. Neural networks containing malignant memories may be the neural mechanism by which perceived abandonment generates such symbolic terror and rage.     

Assessing learning and memory in pigs

In recent years, there has been a surge of interest in (mini) pigs (Sus scrofa) as species for cognitive research. A major reason for this is their physiological and anatomical similarity with humans. For example, pigs possess a well-developed, large brain. Assessment of the learning and memory functions of pigs is not only relevant to human research but also to animal welfare, given the nature of current farming practices and the demands they make on animal health and behavior. In this article, we review studies of pig cognition, focusing on the underlying processes and mechanisms, with a view to identifying. Our goal is to aid the selection of appropriate cognitive tasks for research into pig cognition. To this end, we formulated several basic criteria for pig cognition tests and then applied these criteria and knowledge about pig-specific sensorimotor abilities and behavior to evaluate the merits, drawbacks, and limitations of the different types of tests used to date. While behavioral studies using (mini) pigs have shown that this species can perform learning and memory tasks, and much has been learned about pig cognition, results have not been replicated or proven replicable because of the lack of validated, translational behavioral paradigms that are specially suited to tap specific aspects of pig cognition. We identified several promising types of tasks for use in studies of pig cognition, such as versatile spatial free-choice type tasks that allow the simultaneous measurement of several behavioral domains. The use of appropriate tasks will facilitate the collection of reliable and valid data on pig cognition.     

The neurobiology of substance and behavioral addictions

Behavioral addictions, such as pathological gambling, kleptomania, pyromania, compulsive buying, and compulsive sexual behavior, represent significant public health concerns and are associated with high rates of psychiatric comorbidity and mortality. Although research into the biology of these behaviors is still in the early stages, recent advances in the understanding of motivation, reward, and addiction have provided insight into the possible pathophysiology of these disorders. Biochemical, functional neuroimaging, genetic studies, and treatment research have suggested a strong neurobiological link between behavioral addictions and substance use disorders. Given the substantial co-occurrence of these groups of disorders, improved understanding of their relationship has important implications not only for further understanding the neurobiology of both categories of disorders but also for improving prevention and treatment strategies.     

Aberrant learning and memory in addiction

Over the past several years, drug addiction has increasingly been accepted to be a disease of the brain as opposed to simply being due to a lack of willpower or personality flaw. Exposure to addictive substances has been shown to create enduring changes in brain structure and function that are thought to underlie the transition to addiction. Specific genetic and environmental vulnerability factors also influence the impact of drugs of abuse on the brain and can enhance the likelihood of becoming an addict. Long-lasting alterations in brain function have been found in neural circuits that are known to be responsible for normal appetitive learning and memory processes and it has been hypothesized that drugs of abuse enhance positive learning and memory about the drug while inhibiting learning about the negative consequences of drug use. Therefore, the addict's behavior becomes increasingly directed towards obtaining and using drugs of abuse, while at the same time developing a poorer ability to stop using, even when the drug is less rewarding or interferes with functioning in other facets of life. In this review we will discuss the clinical evidence that addicted individuals have altered learning and memory and describe the possible neural substrates of this dysfunction. In addition, we will explore the pre-clinical evidence that drugs of abuse cause a progressive disorder of learning and memory, review the molecular and neurobiological changes that may underlie this disorder, determine the genetic and environmental factors that may increase vulnerability to addiction, and suggest potential strategies for treating addiction through manipulations of learning and memory.     

Contextual inference in learning and memory

Context is widely regarded as a major determinant of learning and memory across numerous domains, including classical and instrumental conditioning, episodic memory, economic decision-making, and motor learning. However, studies across these domains remain disconnected due to the lack of a unifying framework formalizing the concept of context and its role in learning. Here, we develop a unified vernacular allowing direct comparisons between different domains of contextual learning. This leads to a Bayesian model positing that context is unobserved and needs to be inferred. Contextual inference then controls the creation, expression, and updating of memories. This theoretical approach reveals two distinct components that underlie adaptation, proper and apparent learning, respectively referring to the creation and updating of memories versus time-varying adjustments in their expression. We review a number of extensions of the basic Bayesian model that allow it to account for increasingly complex forms of contextual learning.     

Category learning and multiple memory systems

Categorization is a vitally important skill that people use every day. Early theories of category learning assumed a single learning system, but recent evidence suggests that human category learning may depend on many of the major memory systems that have been hypothesized by memory researchers. As different memory systems flourish under different conditions, an understanding of how categorization uses available memory systems will improve our understanding of a basic human skill, lead to better insights into the cognitive changes that result from a variety of neurological disorders, and suggest improvements in training procedures for complex categorization tasks.